diff --git a/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart b/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
index a8bac9f..9752d91 100644
--- a/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
@@ -1286,9 +1286,6 @@
   /// variable that is no longer in scope.
   final Map<Variable, VariableModel<Variable, Type> /*!*/ > variableInfo;
 
-  /// Variable model for variables that have never been seen before.
-  final VariableModel<Variable, Type> _freshVariableInfo;
-
   /// The empty map, used to [join] variables.
   final Map<Variable, VariableModel<Variable, Type>> _emptyVariableMap = {};
 
@@ -1302,8 +1299,7 @@
         );
 
   @visibleForTesting
-  FlowModel.withInfo(this.reachable, this.variableInfo)
-      : _freshVariableInfo = new VariableModel.fresh() {
+  FlowModel.withInfo(this.reachable, this.variableInfo) {
     assert(reachable != null);
     assert(() {
       for (VariableModel<Variable, Type> value in variableInfo.values) {
@@ -1376,17 +1372,15 @@
   /// A local variable is [initialized] if its declaration has an initializer.
   /// A function parameter is always initialized, so [initialized] is `true`.
   FlowModel<Variable, Type> declare(Variable variable, bool initialized) {
-    VariableModel<Variable, Type> newInfoForVar = _freshVariableInfo;
-    if (initialized) {
-      newInfoForVar = newInfoForVar.initialize();
-    }
+    VariableModel<Variable, Type> newInfoForVar =
+        new VariableModel.fresh(assigned: initialized);
 
     return _updateVariableInfo(variable, newInfoForVar);
   }
 
   /// Gets the info for the given [variable], creating it if it doesn't exist.
   VariableModel<Variable, Type> infoFor(Variable variable) =>
-      variableInfo[variable] ?? _freshVariableInfo;
+      variableInfo[variable] ?? new VariableModel.fresh();
 
   /// Builds a [FlowModel] based on `this`, but extending the `tested` set to
   /// include types from [other].  This is used at the bottom of certain kinds
@@ -2060,11 +2054,10 @@
 
   /// Creates a [VariableModel] representing a variable that's never been seen
   /// before.
-  VariableModel.fresh()
+  VariableModel.fresh({this.assigned = false})
       : promotedTypes = null,
         tested = const [],
-        assigned = false,
-        unassigned = true,
+        unassigned = !assigned,
         writeCaptured = false;
 
   /// Returns a new [VariableModel] in which any promotions present have been
@@ -2077,16 +2070,6 @@
         null, tested, assigned, false, writeCaptured);
   }
 
-  /// Returns a new [VariableModel] reflecting the fact that the variable was
-  /// just initialized.
-  VariableModel<Variable, Type> initialize() {
-    if (promotedTypes == null && tested.isEmpty && assigned && !unassigned) {
-      return this;
-    }
-    return new VariableModel<Variable, Type>(
-        null, const [], true, false, writeCaptured);
-  }
-
   /// Returns an updated model reflect a control path that is known to have
   /// previously passed through some [other] state.  See [FlowModel.restrict]
   /// for details.
diff --git a/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart b/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
index 64581cce..f7adca0 100644
--- a/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
+++ b/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
@@ -3936,7 +3936,9 @@
             Message Function(
                 String name, DartType _type, bool isNonNullableByDefault)>(
         messageTemplate:
-            r"""Optional parameter '#name' should have a default value because its type '#type' doesn't allow null.""",
+            r"""The parameter '#name' can't have a value of 'null' because of its type '#type', but the implicit default value is 'null'.""",
+        tipTemplate:
+            r"""Try adding either an explicit non-'null' default value or the 'required' modifier.""",
         withArguments:
             _withArgumentsOptionalNonNullableWithoutInitializerError);
 
@@ -3945,11 +3947,11 @@
         Message Function(
             String name, DartType _type, bool isNonNullableByDefault)>
     codeOptionalNonNullableWithoutInitializerError = const Code<
-        Message Function(
-            String name, DartType _type, bool isNonNullableByDefault)>(
-  "OptionalNonNullableWithoutInitializerError",
-  templateOptionalNonNullableWithoutInitializerError,
-);
+            Message Function(
+                String name, DartType _type, bool isNonNullableByDefault)>(
+        "OptionalNonNullableWithoutInitializerError",
+        templateOptionalNonNullableWithoutInitializerError,
+        analyzerCodes: <String>["MISSING_DEFAULT_VALUE_FOR_PARAMETER"]);
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 Message _withArgumentsOptionalNonNullableWithoutInitializerError(
@@ -3961,8 +3963,9 @@
   String type = typeParts.join();
   return new Message(codeOptionalNonNullableWithoutInitializerError,
       message:
-          """Optional parameter '${name}' should have a default value because its type '${type}' doesn't allow null.""" +
+          """The parameter '${name}' can't have a value of 'null' because of its type '${type}', but the implicit default value is 'null'.""" +
               labeler.originMessages,
+      tip: """Try adding either an explicit non-'null' default value or the 'required' modifier.""",
       arguments: {'name': name, 'type': _type});
 }
 
diff --git a/pkg/front_end/messages.status b/pkg/front_end/messages.status
index 2fe29ec..2350d4d 100644
--- a/pkg/front_end/messages.status
+++ b/pkg/front_end/messages.status
@@ -629,8 +629,6 @@
 OperatorParameterMismatch2/example: Fail
 OperatorWithOptionalFormals/analyzerCode: Fail
 OperatorWithOptionalFormals/example: Fail
-OptionalNonNullableWithoutInitializerError/analyzerCode: Fail
-OptionalNonNullableWithoutInitializerWarning/analyzerCode: Fail
 OverrideFewerNamedArguments/example: Fail
 OverrideFewerPositionalArguments/example: Fail
 OverrideMismatchNamedParameter/example: Fail
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index ae4a9e7..96f20a7 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -4585,7 +4585,9 @@
   template: "Required named parameter '#name' must be provided."
 
 OptionalNonNullableWithoutInitializerError:
-  template: "Optional parameter '#name' should have a default value because its type '#type' doesn't allow null."
+  template: "The parameter '#name' can't have a value of 'null' because of its type '#type', but the implicit default value is 'null'."
+  tip: "Try adding either an explicit non-'null' default value or the 'required' modifier."
+  analyzerCode: MISSING_DEFAULT_VALUE_FOR_PARAMETER
   configuration: nnbd-strong
   script:
     - method1({int a}) {}
diff --git a/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.outline.expect b/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.outline.expect
index 7171bac..e60e513 100644
--- a/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.outline.expect
+++ b/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.outline.expect
@@ -22,7 +22,8 @@
 //   const Class.method(T t) : this(-t);
 //                                  ^
 //
-// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: Optional parameter 'named' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: The parameter 'named' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // int procedure(int i, {int named}) => i;
 //                           ^^^^^
 //
diff --git a/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.expect b/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.expect
index aa1a131..8f2590a 100644
--- a/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.expect
+++ b/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.expect
@@ -22,7 +22,8 @@
 //   const Class.method(T t) : this(-t);
 //                                  ^
 //
-// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: Optional parameter 'named' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: The parameter 'named' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // int procedure(int i, {int named}) => i;
 //                           ^^^^^
 //
diff --git a/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.transformed.expect b/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.transformed.expect
index 9d5946b..858bb47 100644
--- a/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart.strong.transformed.expect
@@ -22,7 +22,8 @@
 //   const Class.method(T t) : this(-t);
 //                                  ^
 //
-// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: Optional parameter 'named' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/general/constants/with_unevaluated_agnostic/various.dart:123:27: Error: The parameter 'named' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // int procedure(int i, {int named}) => i;
 //                           ^^^^^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue40954.dart.outline.expect b/pkg/front_end/testcases/nnbd/issue40954.dart.outline.expect
index c6641b9..35e6233 100644
--- a/pkg/front_end/testcases/nnbd/issue40954.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/issue40954.dart.outline.expect
@@ -2,33 +2,39 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue40954.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue40954.dart.strong.expect
index e94c384..cbfe037 100644
--- a/pkg/front_end/testcases/nnbd/issue40954.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue40954.dart.strong.expect
@@ -2,33 +2,39 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue40954.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue40954.dart.strong.transformed.expect
index e94c384..cbfe037 100644
--- a/pkg/front_end/testcases/nnbd/issue40954.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue40954.dart.strong.transformed.expect
@@ -2,33 +2,39 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue40954.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue40954.dart.weak.expect
index e94c384..cbfe037 100644
--- a/pkg/front_end/testcases/nnbd/issue40954.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue40954.dart.weak.expect
@@ -2,33 +2,39 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue40954.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue40954.dart.weak.transformed.expect
index e94c384..cbfe037 100644
--- a/pkg/front_end/testcases/nnbd/issue40954.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue40954.dart.weak.transformed.expect
@@ -2,33 +2,39 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:8:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test1(var v, [A a]) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:10:31: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   static void test2(var v, {A a}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:12:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test11(var v, [A a]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:14:25: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void test22(var v, {A a}) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:17:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test1(var v, [A a]) {}
 //                      ^
 //
-// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: Optional parameter 'a' should have a default value because its type 'A' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue40954.dart:19:22: Error: The parameter 'a' can't have a value of 'null' because of its type 'A', but the implicit default value is 'null'.
 //  - 'A' is from 'pkg/front_end/testcases/nnbd/issue40954.dart'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void test2(var v, {A a}) {}
 //                      ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue42362.dart.outline.expect b/pkg/front_end/testcases/nnbd/issue42362.dart.outline.expect
index 36632a1..dbb74c3 100644
--- a/pkg/front_end/testcases/nnbd/issue42362.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/issue42362.dart.outline.expect
@@ -2,67 +2,83 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([int i]) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({int i}) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor3([int i]) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor4({int i}) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory8([int i]) => new A.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory9({int i}) => new A.constructor4(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([i]) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({i}) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor3([int i]) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor4({int i}) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory8([int i]) => new C.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory9({int i}) => new C.constructor4(); // error
 //                           ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue42362.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue42362.dart.strong.expect
index 0f40eb2..327d48b 100644
--- a/pkg/front_end/testcases/nnbd/issue42362.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue42362.dart.strong.expect
@@ -2,67 +2,83 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([int i]) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({int i}) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor3([int i]) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor4({int i}) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory8([int i]) => new A.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory9({int i}) => new A.constructor4(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([i]) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({i}) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor3([int i]) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor4({int i}) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory8([int i]) => new C.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory9({int i}) => new C.constructor4(); // error
 //                           ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue42362.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue42362.dart.strong.transformed.expect
index 2d7d920..d74b206 100644
--- a/pkg/front_end/testcases/nnbd/issue42362.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue42362.dart.strong.transformed.expect
@@ -2,67 +2,83 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([int i]) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({int i}) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor3([int i]) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor4({int i}) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory8([int i]) => new A.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory9({int i}) => new A.constructor4(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([i]) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({i}) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor3([int i]) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor4({int i}) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory8([int i]) => new C.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory9({int i}) => new C.constructor4(); // error
 //                           ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue42362.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue42362.dart.weak.expect
index 0f40eb2..327d48b 100644
--- a/pkg/front_end/testcases/nnbd/issue42362.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue42362.dart.weak.expect
@@ -2,67 +2,83 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([int i]) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({int i}) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor3([int i]) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor4({int i}) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory8([int i]) => new A.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory9({int i}) => new A.constructor4(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([i]) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({i}) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor3([int i]) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor4({int i}) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory8([int i]) => new C.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory9({int i}) => new C.constructor4(); // error
 //                           ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue42362.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue42362.dart.weak.transformed.expect
index 253c393..9e8520e 100644
--- a/pkg/front_end/testcases/nnbd/issue42362.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue42362.dart.weak.transformed.expect
@@ -2,67 +2,83 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:45:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([int i]) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:47:16: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({int i}) {} // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:8:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:10:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:12:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor3([int i]) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:15:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   A.constructor4({int i}) // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:41:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory8([int i]) => new A.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:43:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory A.factory9({int i}) => new A.constructor4(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:106:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method3([i]) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:108:12: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   method4({i}) {} // error
 //            ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:77:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor1([this.i]); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:79:24: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor2({this.i}); // error
 //                        ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:81:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor3([int i]) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:83:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.constructor4({int i}) : this.i = i; // error
 //                       ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:102:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory8([int i]) => new C.constructor3(); // error
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue42362.dart:104:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.factory9({int i}) => new C.constructor4(); // error
 //                           ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue43276.dart.outline.expect b/pkg/front_end/testcases/nnbd/issue43276.dart.outline.expect
index 9cbb91e..83d2e51 100644
--- a/pkg/front_end/testcases/nnbd/issue43276.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/issue43276.dart.outline.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.gen({int i}); // error
 //              ^
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.fact({int i}) /* error */ {
 //                       ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue43276.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue43276.dart.strong.expect
index dfcedf7..bcb7771 100644
--- a/pkg/front_end/testcases/nnbd/issue43276.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue43276.dart.strong.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.gen({int i}); // error
 //              ^
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.fact({int i}) /* error */ {
 //                       ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue43276.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue43276.dart.strong.transformed.expect
index ac206c0..744265d 100644
--- a/pkg/front_end/testcases/nnbd/issue43276.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue43276.dart.strong.transformed.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.gen({int i}); // error
 //              ^
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.fact({int i}) /* error */ {
 //                       ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue43276.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue43276.dart.weak.expect
index dfcedf7..bcb7771 100644
--- a/pkg/front_end/testcases/nnbd/issue43276.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue43276.dart.weak.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.gen({int i}); // error
 //              ^
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.fact({int i}) /* error */ {
 //                       ^
 //
diff --git a/pkg/front_end/testcases/nnbd/issue43276.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue43276.dart.weak.transformed.expect
index ac206c0..744265d 100644
--- a/pkg/front_end/testcases/nnbd/issue43276.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue43276.dart.weak.transformed.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:6:14: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   C.gen({int i}); // error
 //              ^
 //
-// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/issue43276.dart:8:23: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   factory C.fact({int i}) /* error */ {
 //                       ^
 //
diff --git a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.outline.expect b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.outline.expect
index f59fb9e..9089964 100644
--- a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.outline.expect
@@ -2,19 +2,23 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method1({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method2([int a]) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method3({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method4([int a]) {}
 //              ^
 //
diff --git a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.expect b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.expect
index d869c59..f03bd13 100644
--- a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.expect
@@ -2,19 +2,23 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method1({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method2([int a]) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method3({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method4([int a]) {}
 //              ^
 //
diff --git a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.transformed.expect
index d869c59..f03bd13 100644
--- a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.strong.transformed.expect
@@ -2,19 +2,23 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method1({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method2([int a]) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method3({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method4([int a]) {}
 //              ^
 //
diff --git a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.expect b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.expect
index d869c59..f03bd13 100644
--- a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.expect
@@ -2,19 +2,23 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method1({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method2([int a]) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method3({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method4([int a]) {}
 //              ^
 //
diff --git a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.transformed.expect
index d869c59..f03bd13 100644
--- a/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/non_nullable_optional.dart.weak.transformed.expect
@@ -2,19 +2,23 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method1({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional.dart:11:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method2([int a]) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:7:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method3({int a}) {}
 //              ^
 //
-// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/non_nullable_optional_part.dart:9:14: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // method4([int a]) {}
 //              ^
 //
diff --git a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.outline.expect b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.outline.expect
index 6a9e27e..49eec30 100644
--- a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.outline.expect
@@ -10,27 +10,33 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void patchedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void _injectedMethod([int i]) {}
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void patchedMethod([int i]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void _injectedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void method([int i]) {}
 //                    ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void method([int i]) {}
 //                  ^
 //
diff --git a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.expect b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.expect
index 9762f48..2d71c44 100644
--- a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.expect
@@ -12,27 +12,33 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void patchedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void _injectedMethod([int i]) {}
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void patchedMethod([int i]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void _injectedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void method([int i]) {}
 //                    ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void method([int i]) {}
 //                  ^
 //
diff --git a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.transformed.expect
index 9762f48..2d71c44 100644
--- a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.strong.transformed.expect
@@ -12,27 +12,33 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void patchedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void _injectedMethod([int i]) {}
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void patchedMethod([int i]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void _injectedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void method([int i]) {}
 //                    ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void method([int i]) {}
 //                  ^
 //
diff --git a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.expect b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.expect
index 9762f48..2d71c44 100644
--- a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.expect
@@ -12,27 +12,33 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void patchedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void _injectedMethod([int i]) {}
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void patchedMethod([int i]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void _injectedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void method([int i]) {}
 //                    ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void method([int i]) {}
 //                  ^
 //
diff --git a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.transformed.expect
index 9762f48..2d71c44 100644
--- a/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/platform_optional_parameters/main.dart.weak.transformed.expect
@@ -12,27 +12,33 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:11:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void patchedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:13:29: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void _injectedMethod([int i]) {}
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:17:25: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void patchedMethod([int i]) {}
 //                         ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/patch_lib.dart:19:27: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void _injectedMethod([int i]) {}
 //                           ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:6:20: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void method([int i]) {}
 //                    ^
 //
-// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: Optional parameter 'i' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/platform_optional_parameters/origin_lib.dart:11:18: Error: The parameter 'i' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // void method([int i]) {}
 //                  ^
 //
diff --git a/pkg/front_end/testcases/nnbd/required.dart.outline.expect b/pkg/front_end/testcases/nnbd/required.dart.outline.expect
index ff5e088..f5a1db6 100644
--- a/pkg/front_end/testcases/nnbd/required.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/required.dart.outline.expect
@@ -2,7 +2,8 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: Optional parameter 'x' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: The parameter 'x' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   foo({x}) {}
 //        ^
 //
diff --git a/pkg/front_end/testcases/nnbd/required.dart.strong.expect b/pkg/front_end/testcases/nnbd/required.dart.strong.expect
index 55eb694..dfe4abf 100644
--- a/pkg/front_end/testcases/nnbd/required.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/required.dart.strong.expect
@@ -2,7 +2,8 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: Optional parameter 'x' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: The parameter 'x' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   foo({x}) {}
 //        ^
 //
@@ -21,7 +22,8 @@
 //   f2 = (int a = 42, [int b]) {};
 //               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g({int a, required int b = 42}) {}
 //               ^
 //
@@ -29,7 +31,8 @@
 //   void g({int a, required int b = 42}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f = ({int a, required int b = 42}) {};
 //             ^
 //
@@ -37,11 +40,13 @@
 //   f = ({int a, required int b = 42}) {};
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g2(int a = 42, [int b]) {}
 //                            ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f2 = (int a = 42, [int b]) {};
 //                          ^
 //
diff --git a/pkg/front_end/testcases/nnbd/required.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/required.dart.strong.transformed.expect
index 55eb694..dfe4abf 100644
--- a/pkg/front_end/testcases/nnbd/required.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/required.dart.strong.transformed.expect
@@ -2,7 +2,8 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: Optional parameter 'x' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: The parameter 'x' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   foo({x}) {}
 //        ^
 //
@@ -21,7 +22,8 @@
 //   f2 = (int a = 42, [int b]) {};
 //               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g({int a, required int b = 42}) {}
 //               ^
 //
@@ -29,7 +31,8 @@
 //   void g({int a, required int b = 42}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f = ({int a, required int b = 42}) {};
 //             ^
 //
@@ -37,11 +40,13 @@
 //   f = ({int a, required int b = 42}) {};
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g2(int a = 42, [int b]) {}
 //                            ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f2 = (int a = 42, [int b]) {};
 //                          ^
 //
diff --git a/pkg/front_end/testcases/nnbd/required.dart.weak.expect b/pkg/front_end/testcases/nnbd/required.dart.weak.expect
index 55eb694..dfe4abf 100644
--- a/pkg/front_end/testcases/nnbd/required.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/required.dart.weak.expect
@@ -2,7 +2,8 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: Optional parameter 'x' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: The parameter 'x' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   foo({x}) {}
 //        ^
 //
@@ -21,7 +22,8 @@
 //   f2 = (int a = 42, [int b]) {};
 //               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g({int a, required int b = 42}) {}
 //               ^
 //
@@ -29,7 +31,8 @@
 //   void g({int a, required int b = 42}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f = ({int a, required int b = 42}) {};
 //             ^
 //
@@ -37,11 +40,13 @@
 //   f = ({int a, required int b = 42}) {};
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g2(int a = 42, [int b]) {}
 //                            ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f2 = (int a = 42, [int b]) {};
 //                          ^
 //
diff --git a/pkg/front_end/testcases/nnbd/required.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/required.dart.weak.transformed.expect
index 55eb694..dfe4abf 100644
--- a/pkg/front_end/testcases/nnbd/required.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/required.dart.weak.transformed.expect
@@ -2,7 +2,8 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: Optional parameter 'x' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:29:8: Error: The parameter 'x' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   foo({x}) {}
 //        ^
 //
@@ -21,7 +22,8 @@
 //   f2 = (int a = 42, [int b]) {};
 //               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:48:15: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g({int a, required int b = 42}) {}
 //               ^
 //
@@ -29,7 +31,8 @@
 //   void g({int a, required int b = 42}) {}
 //                               ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: Optional parameter 'a' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:49:13: Error: The parameter 'a' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f = ({int a, required int b = 42}) {};
 //             ^
 //
@@ -37,11 +40,13 @@
 //   f = ({int a, required int b = 42}) {};
 //                             ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:52:28: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   void g2(int a = 42, [int b]) {}
 //                            ^
 //
-// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: Optional parameter 'b' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required.dart:53:26: Error: The parameter 'b' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   f2 = (int a = 42, [int b]) {};
 //                          ^
 //
diff --git a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.outline.expect b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.outline.expect
index 8dab663..4e786d8 100644
--- a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.outline.expect
@@ -6,11 +6,13 @@
 // foo({required int parameter = 42}) {}
 //                   ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo2({int parameter}) {}
 //           ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo3([int parameter]) {}
 //           ^^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.expect b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.expect
index 41566f3..0f14fea 100644
--- a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.expect
@@ -6,11 +6,13 @@
 // foo({required int parameter = 42}) {}
 //                   ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo2({int parameter}) {}
 //           ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo3([int parameter]) {}
 //           ^^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.transformed.expect
index 41566f3..0f14fea 100644
--- a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.strong.transformed.expect
@@ -6,11 +6,13 @@
 // foo({required int parameter = 42}) {}
 //                   ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo2({int parameter}) {}
 //           ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo3([int parameter]) {}
 //           ^^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.expect b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.expect
index 41566f3..0f14fea 100644
--- a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.expect
@@ -6,11 +6,13 @@
 // foo({required int parameter = 42}) {}
 //                   ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo2({int parameter}) {}
 //           ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo3([int parameter]) {}
 //           ^^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.transformed.expect
index 41566f3..0f14fea 100644
--- a/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/required_named_parameter.dart.weak.transformed.expect
@@ -6,11 +6,13 @@
 // foo({required int parameter = 42}) {}
 //                   ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:7:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo2({int parameter}) {}
 //           ^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: Optional parameter 'parameter' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/nnbd/required_named_parameter.dart:8:11: Error: The parameter 'parameter' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 // foo3([int parameter]) {}
 //           ^^^^^^^^^
 //
diff --git a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.outline.expect b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.outline.expect
index 93422d0..f6aa033 100644
--- a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.outline.expect
+++ b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.outline.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: Optional parameter 'bar' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: The parameter 'bar' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                     ^^^
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: Optional parameter 'bar2' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: The parameter 'bar2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                              ^^^^
 //
diff --git a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.expect b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.expect
index 1f7ce47..4449dd3 100644
--- a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.expect
+++ b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: Optional parameter 'bar' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: The parameter 'bar' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                     ^^^
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: Optional parameter 'bar2' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: The parameter 'bar2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                              ^^^^
 //
diff --git a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.transformed.expect b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.transformed.expect
index db25a4a..57c58e3 100644
--- a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.strong.transformed.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: Optional parameter 'bar' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: The parameter 'bar' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                     ^^^
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: Optional parameter 'bar2' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: The parameter 'bar2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                              ^^^^
 //
diff --git a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.expect b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.expect
index 1f7ce47..4449dd3 100644
--- a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.expect
+++ b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: Optional parameter 'bar' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: The parameter 'bar' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                     ^^^
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: Optional parameter 'bar2' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: The parameter 'bar2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                              ^^^^
 //
diff --git a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.transformed.expect b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.transformed.expect
index db25a4a..57c58e3 100644
--- a/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/value_class/copy_with_call_sites.dart.weak.transformed.expect
@@ -2,11 +2,13 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: Optional parameter 'bar' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:21: Error: The parameter 'bar' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                     ^^^
 //
-// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: Optional parameter 'bar2' should have a default value because its type 'int' doesn't allow null.
+// pkg/front_end/testcases/value_class/copy_with_call_sites.dart:20:30: Error: The parameter 'bar2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'.
+// Try adding either an explicit non-'null' default value or the 'required' modifier.
 //   Foo copyWith({int bar, int bar2}) {
 //                              ^^^^
 //
diff --git a/runtime/vm/compiler/frontend/scope_builder.cc b/runtime/vm/compiler/frontend/scope_builder.cc
index ea6b457..ba75d00 100644
--- a/runtime/vm/compiler/frontend/scope_builder.cc
+++ b/runtime/vm/compiler/frontend/scope_builder.cc
@@ -1274,7 +1274,7 @@
   // debuggable position in the initializer.
   TokenPosition end_position = helper_.reader_.max_position();
   if (end_position.IsReal()) {
-    end_position.Next();
+    end_position = end_position.Next();
   }
   LocalVariable* variable =
       MakeVariable(helper.position_, end_position, name, type);
diff --git a/runtime/vm/debugger.cc b/runtime/vm/debugger.cc
index 5f3ca29..d1096d7 100644
--- a/runtime/vm/debugger.cc
+++ b/runtime/vm/debugger.cc
@@ -3033,7 +3033,7 @@
   while ((loc == NULL) && (first_token_idx <= last_token_idx)) {
     loc = SetBreakpoint(script, first_token_idx, last_token_idx, line_number,
                         column_number, Function::Handle());
-    first_token_idx.Next();
+    first_token_idx = first_token_idx.Next();
   }
   if ((loc == NULL) && FLAG_verbose_debug) {
     OS::PrintErr("No executable code at line %" Pd " in '%s'\n", line_number,
diff --git a/runtime/vm/token_position.cc b/runtime/vm/token_position.cc
index b94ddff..0f8ae68 100644
--- a/runtime/vm/token_position.cc
+++ b/runtime/vm/token_position.cc
@@ -27,12 +27,12 @@
 }
 
 #define DEFINE_VALUES(name, value)                                             \
-  const TokenPosition TokenPosition::k##name = TokenPosition(value);
+  const TokenPosition TokenPosition::k##name(value);
 SENTINEL_TOKEN_DESCRIPTORS(DEFINE_VALUES);
 #undef DEFINE_VALUES
-const TokenPosition TokenPosition::kMinSource = TokenPosition(kMinSourcePos);
+const TokenPosition TokenPosition::kMinSource(kMinSourcePos);
 
-const TokenPosition TokenPosition::kMaxSource = TokenPosition(kMaxSourcePos);
+const TokenPosition TokenPosition::kMaxSource(kMaxSourcePos);
 
 const char* TokenPosition::ToCString() const {
   switch (value_) {
diff --git a/runtime/vm/token_position.h b/runtime/vm/token_position.h
index c28f9a4..270a14c 100644
--- a/runtime/vm/token_position.h
+++ b/runtime/vm/token_position.h
@@ -95,11 +95,10 @@
   // Encode for writing into a snapshot.
   int32_t SnapshotEncode();
 
-  // Increment the token position.
+  // Given a real token position, returns the next real token position.
   TokenPosition Next() {
     ASSERT(IsReal());
-    value_++;
-    return *this;
+    return TokenPosition(value_ + 1);
   }
 
   // The raw value.
diff --git a/sdk/lib/_internal/vm/bin/socket_patch.dart b/sdk/lib/_internal/vm/bin/socket_patch.dart
index d567603..f2a91d8 100644
--- a/sdk/lib/_internal/vm/bin/socket_patch.dart
+++ b/sdk/lib/_internal/vm/bin/socket_patch.dart
@@ -574,16 +574,28 @@
 
   static Future<ConnectionTask<_NativeSocket>> startConnect(
       dynamic host, int port, dynamic sourceAddress) {
+    // Looks up [sourceAddress] to one or more IP addresses,
+    // then tries connecting to each one until a connection succeeds.
+    // Attempts are staggered by a minimum delay, so a new
+    // attempt isn't made until either a previous attempt has *failed*,
+    // or the delay has passed.
+    // This ensures that at most *n* uncompleted connections can be
+    // active after *n* &times; *delay* time has passed.
     if (host is String) {
       host = escapeLinkLocalAddress(host);
     }
     _throwOnBadPort(port);
-    if (sourceAddress != null && sourceAddress is! _InternetAddress) {
-      if (sourceAddress is String) {
-        sourceAddress = new InternetAddress(sourceAddress);
-      }
+    _InternetAddress? source;
+    if (sourceAddress is _InternetAddress) {
+      source = sourceAddress;
+    } else if (sourceAddress is String) {
+      source = new _InternetAddress.fromString(sourceAddress);
     }
-    return new Future.value(host).then((host) {
+    // Should we throw if sourceAddress is not one of:
+    // null, _InternetAddress or String?
+    // Is it somehow ensured upstream
+    // that only those three types will reach here?
+    return new Future.value(host).then<List<InternetAddress>>((host) {
       if (host is _InternetAddress) return [host];
       return lookup(host).then((addresses) {
         if (addresses.isEmpty) {
@@ -592,23 +604,43 @@
         return addresses;
       });
     }).then((addresses) {
+      assert(addresses.isNotEmpty);
+      // Completer for result.
       var completer = new Completer<_NativeSocket>();
-      var it = (addresses as List<InternetAddress>).iterator;
+      // Index of next address in [addresses] to try.
+      var index = 0;
+      // Error, set if an error occurs.
+      // Keeps first error if multiple errors occour.
       var error = null;
-      var connecting = new HashMap();
+      // Active timers for on-going connection attempts.
+      // Contains all sockets which haven't received and initial
+      // write or error event.
+      var connecting = <_NativeSocket>{};
+      // Timer counting down from the last connection attempt.
+      // Reset when a new connection is attempted,
+      // which happens either when a previous timer runs out,
+      // or when a previous connection attempt fails.
+      Timer? timer;
 
+      // Attempt to connect to the next address in [addresses].
+      //
+      // Called initially, then when either a connection attempt fails,
+      // or an amount of time has passed since the last connection
+      // was attempted.
       void connectNext() {
-        if (!it.moveNext()) {
+        timer?.cancel();
+        if (index >= addresses.length) {
           if (connecting.isEmpty) {
             assert(error != null);
+            assert(!completer.isCompleted);
             completer.completeError(error);
           }
           return;
         }
-        final _InternetAddress address = it.current as _InternetAddress;
+        final address = addresses[index++] as _InternetAddress;
         var socket = new _NativeSocket.normal(address);
         var result;
-        if (sourceAddress == null) {
+        if (source == null) {
           if (address.type == InternetAddressType.unix) {
             result = socket.nativeCreateUnixDomainConnect(
                 address.address, _Namespace._namespace);
@@ -617,97 +649,103 @@
                 address._in_addr, port, address._scope_id);
           }
         } else {
-          assert(sourceAddress is _InternetAddress);
           if (address.type == InternetAddressType.unix) {
-            assert(sourceAddress.type == InternetAddressType.unix);
+            assert(source.type == InternetAddressType.unix);
             result = socket.nativeCreateUnixDomainBindConnect(
-                address.address, sourceAddress.address, _Namespace._namespace);
+                address.address, source.address, _Namespace._namespace);
           } else {
-            result = socket.nativeCreateBindConnect(address._in_addr, port,
-                sourceAddress._in_addr, address._scope_id);
+            result = socket.nativeCreateBindConnect(
+                address._in_addr, port, source._in_addr, address._scope_id);
           }
         }
         if (result is OSError) {
           // Keep first error, if present.
           if (error == null) {
             int errorCode = result.errorCode;
-            if (sourceAddress != null &&
+            if (source != null &&
                 errorCode != null &&
                 socket.isBindError(errorCode)) {
-              error = createError(result, "Bind failed", sourceAddress);
+              error = createError(result, "Bind failed", source);
             } else {
               error = createError(result, "Connection failed", address, port);
             }
           }
-          connectNext();
-        } else {
-          // Query the local port for error messages.
-          try {
-            socket.port;
-          } catch (e) {
-            if (error == null) {
-              error = createError(e, "Connection failed", address, port);
-            }
-            connectNext();
-          }
-          // Set up timer for when we should retry the next address
-          // (if any).
-          var duration =
-              address.isLoopback ? _retryDurationLoopback : _retryDuration;
-          var timer = new Timer(duration, connectNext);
-
-          connecting[socket] = timer;
-          // Setup handlers for receiving the first write event which
-          // indicate that the socket is fully connected.
-          socket.setHandlers(write: () {
-            timer.cancel();
-            connecting.remove(socket);
-            // From 'man 2 connect':
-            // After select(2) indicates writability, use getsockopt(2) to read
-            // the SO_ERROR option at level SOL_SOCKET to determine whether
-            // connect() completed successfully (SO_ERROR is zero) or
-            // unsuccessfully.
-            OSError osError = socket.nativeGetError();
-            if (osError.errorCode != 0) {
-              socket.close();
-              if (error == null) error = osError;
-              if (connecting.isEmpty) connectNext();
-              return;
-            }
-            socket.setListening(read: false, write: false);
-            completer.complete(socket);
-            connecting.forEach((s, t) {
-              t.cancel();
-              s.close();
-              s.setHandlers();
-              s.setListening(read: false, write: false);
-            });
-            connecting.clear();
-          }, error: (e, st) {
-            timer.cancel();
-            socket.close();
-            // Keep first error, if present.
-            if (error == null) error = e;
-            connecting.remove(socket);
-            if (connecting.isEmpty) connectNext();
-          });
-          socket.setListening(read: false, write: true);
+          connectNext(); // Try again after failure to connect.
+          return;
         }
+        // Query the local port for error messages.
+        try {
+          socket.port;
+        } catch (e) {
+          if (error == null) {
+            error = createError(e, "Connection failed", address, port);
+          }
+          connectNext(); // Try again after failure to connect.
+          return;
+        }
+
+        // Try again if no response (failure or success) within a duration.
+        // If this occurs, the socket is still trying to connect, and might
+        // succeed or fail later.
+        var duration =
+            address.isLoopback ? _retryDurationLoopback : _retryDuration;
+        timer = new Timer(duration, connectNext);
+
+        connecting.add(socket);
+        // Setup handlers for receiving the first write event which
+        // indicate that the socket is fully connected.
+        socket.setHandlers(write: () {
+          // First remote response on connection.
+          // If error, drop the socket and go to the next address.
+          // If success, complete with the socket
+          // and stop all other open connection attempts.
+          connecting.remove(socket);
+          // From 'man 2 connect':
+          // After select(2) indicates writability, use getsockopt(2) to read
+          // the SO_ERROR option at level SOL_SOCKET to determine whether
+          // connect() completed successfully (SO_ERROR is zero) or
+          // unsuccessfully.
+          OSError osError = socket.nativeGetError();
+          if (osError.errorCode != 0) {
+            socket.close();
+            error ??= osError;
+            connectNext(); // Try again after failure to connect.
+            return;
+          }
+          // Connection success!
+          // Stop all other connecting sockets and timers.
+          timer!.cancel();
+          socket.setListening(read: false, write: false);
+          for (var s in connecting) {
+            s.close();
+            s.setHandlers();
+            s.setListening(read: false, write: false);
+          }
+          connecting.clear();
+          completer.complete(socket);
+        }, error: (e, st) {
+          connecting.remove(socket);
+          socket.close();
+          socket.setHandlers();
+          socket.setListening(read: false, write: false);
+          // Keep first error, if present.
+          error ??= e;
+          connectNext(); // Try again after failure to connect.
+        });
+        socket.setListening(read: false, write: true);
       }
 
       void onCancel() {
-        connecting.forEach((s, t) {
-          t.cancel();
+        timer?.cancel();
+        for (var s in connecting) {
           s.close();
           s.setHandlers();
           s.setListening(read: false, write: false);
-          if (error == null) {
-            error = createError(null,
-                "Connection attempt cancelled, host: ${host}, port: ${port}");
-          }
-        });
+        }
         connecting.clear();
         if (!completer.isCompleted) {
+          error ??= createError(null,
+              "Connection attempt cancelled, host: ${host}, port: ${port}");
           completer.completeError(error);
         }
       }
diff --git a/tools/VERSION b/tools/VERSION
index c3af410..ac2b734 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 12
 PATCH 0
-PRERELEASE 111
+PRERELEASE 112
 PRERELEASE_PATCH 0
\ No newline at end of file