library /*isNonNullableByDefault*/;
//
// Problems in library:
//
// pkg/front_end/testcases/nnbd/return_null.dart:7:8: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
// String returnImplicit() /*error*/ {
//        ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:13:10: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
//   return null; // error
//          ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:19:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
//     return null; // error
//            ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:16:8: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
// String returnMixed(bool b) /*error*/ {
//        ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:27:15: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
// FutureOr<int> returnAsync3() async {} // error
//               ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
//  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
// Enum caseReturn2(Enum e) /* error */ {
//      ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
//   String returnImplicit() /* error */ {
//   ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
//     return null; // error
//            ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
//       return null; // error
//              ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
//   String returnMixed(bool b) /* error */ {
//   ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
//   FutureOr<int> returnAsync3() async {} // error
//   ^
//
// pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
//  - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
//   Enum caseReturn2(Enum e) /* error */ {
//   ^
//
import self as self;
import "dart:core" as core;
import "dart:async" as asy;
import "dart:_internal" as _in;

import "dart:async";

class Enum extends core::Object /*isEnum*/  {
  final field core::int index;
  final field core::String _name;
  static const field core::List<self::Enum> values = #C7;
  static const field self::Enum a = #C3;
  static const field self::Enum b = #C6;
  const constructor •(core::int index, core::String _name) → self::Enum
    : self::Enum::index = index, self::Enum::_name = _name, super core::Object::•()
    ;
  method toString() → core::String
    return this.{self::Enum::_name};
}
static method returnImplicit() → core::String {
  core::print("foo");
  return let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:7:8: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
String returnImplicit() /*error*/ {
       ^" in null;
}
static method returnExplicit() → core::String {
  core::print("foo");
  return let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:13:10: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
  return null; // error
         ^" in null;
}
static method returnMixed(core::bool b) → core::String {
  if(b) {
    core::print("foo");
    return let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:19:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
    return null; // error
           ^" in null;
  }
  return let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:16:8: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
String returnMixed(bool b) /*error*/ {
       ^" in null;
}
static method returnAsync1() → asy::Future<dynamic> /* originally async */ {
  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
  core::bool* :is_sync = false;
  FutureOr<dynamic>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L1:
      {}
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method returnAsync2() → FutureOr<dynamic> /* originally async */ {
  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
  core::bool* :is_sync = false;
  FutureOr<dynamic>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L2:
      {}
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method returnAsync3() → FutureOr<core::int> /* originally async */ {
  final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
  core::bool* :is_sync = false;
  FutureOr<core::int>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L3:
      {
        :return_value = let final<BottomType> #t5 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:27:15: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
FutureOr<int> returnAsync3() async {} // error
              ^" in null;
        break #L3;
      }
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method returnAsync4() → FutureOr<core::int?> /* originally async */ {
  final asy::_Future<core::int?> :async_future = new asy::_Future::•<core::int?>();
  core::bool* :is_sync = false;
  FutureOr<core::int?>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L4:
      {}
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method returnAsync5() → dynamic /* originally async */ {
  final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
  core::bool* :is_sync = false;
  FutureOr<dynamic>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L5:
      {}
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method returnAsync6() → asy::Future<core::int?> /* originally async */ {
  final asy::_Future<core::int?> :async_future = new asy::_Future::•<core::int?>();
  core::bool* :is_sync = false;
  FutureOr<core::int?>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L6:
      {
        :return_value = null;
        break #L6;
      }
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method returnAsync7() → asy::Future<core::int?> /* originally async */ {
  final asy::_Future<core::int?> :async_future = new asy::_Future::•<core::int?>();
  core::bool* :is_sync = false;
  FutureOr<core::int?>? :return_value;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try {
      #L7:
      {}
      asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
      return;
    }
    on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
      asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :async_op.call();
  :is_sync = true;
  return :async_future;
}
static method yieldSync() → core::Iterable<dynamic> /* originally sync* */ {
  function :sync_op_gen() → (core::_SyncIterator<dynamic>?, dynamic, dynamic) → core::bool* {
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :sync_op(core::_SyncIterator<dynamic>? :iterator, dynamic :exception, dynamic :stack_trace) → core::bool* yielding {
      {}
      return false;
    }
    return :sync_op;
  }
  return new core::_SyncIterable::•<dynamic>(:sync_op_gen);
}
static method yieldAsync() → asy::Stream<dynamic> /* originally async* */ {
  asy::_AsyncStarStreamController<dynamic>? :controller;
  dynamic :controller_stream;
  (dynamic) → dynamic :async_op_then;
  (core::Object, core::StackTrace) → dynamic :async_op_error;
  core::int :await_jump_var = 0;
  dynamic :await_ctx_var;
  function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
    try
      try {
        #L8:
        {}
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        :controller.{asy::_AsyncStarStreamController::addError}(exception, stack_trace);
      }
    finally {
      :controller.{asy::_AsyncStarStreamController::close}();
    }
  :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
  :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
  :controller = new asy::_AsyncStarStreamController::•<dynamic>(:async_op);
  :controller_stream = :controller.{asy::_AsyncStarStreamController::stream};
  return :controller_stream;
}
static method caseReturn1(self::Enum e) → self::Enum {
  switch(e) {
    #L9:
    case #C3:
      {
        return e;
      }
    #L10:
    case #C6:
      {
        return e;
      }
    #L11:
    default:
      throw new _in::ReachabilityError::•("`null` encountered as case in a switch expression with a non-nullable enum type.");
  }
}
static method caseReturn2(self::Enum e) → self::Enum {
  switch(e) {
    #L12:
    case #C3:
      {
        return e;
      }
    #L13:
    default:
      {}
  }
  return let final<BottomType> #t6 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:54:6: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
 - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
Enum caseReturn2(Enum e) /* error */ {
     ^" in null;
}
static method localFunctions() → dynamic {
  function returnImplicit() → core::String {
    core::print("foo");
    return let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:63:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
  String returnImplicit() /* error */ {
  ^" in null;
  }
  function returnExplicit() → core::String {
    core::print("foo");
    return let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:69:12: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
    return null; // error
           ^" in null;
  }
  function returnMixed(core::bool b) → core::String {
    if(b) {
      core::print("foo");
      return let final<BottomType> #t9 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:75:14: Error: The value 'null' can't be returned from a function with return type 'String' because 'String' is not nullable.
      return null; // error
             ^" in null;
    }
    return let final<BottomType> #t10 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:72:3: Error: A non-null value must be returned since the return type 'String' doesn't allow null.
  String returnMixed(bool b) /* error */ {
  ^" in null;
  }
  function returnAsync1() → asy::Future<dynamic> /* originally async */ {
    final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
    core::bool* :is_sync = false;
    FutureOr<dynamic>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L14:
        {}
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function returnAsync2() → FutureOr<dynamic> /* originally async */ {
    final asy::_Future<dynamic> :async_future = new asy::_Future::•<dynamic>();
    core::bool* :is_sync = false;
    FutureOr<dynamic>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L15:
        {}
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function returnAsync3() → FutureOr<core::int> /* originally async */ {
    final asy::_Future<core::int> :async_future = new asy::_Future::•<core::int>();
    core::bool* :is_sync = false;
    FutureOr<core::int>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L16:
        {
          :return_value = let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:83:3: Error: A non-null value must be returned since the return type 'int' doesn't allow null.
  FutureOr<int> returnAsync3() async {} // error
  ^" in null;
          break #L16;
        }
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function returnAsync4() → FutureOr<core::int?> /* originally async */ {
    final asy::_Future<core::int?> :async_future = new asy::_Future::•<core::int?>();
    core::bool* :is_sync = false;
    FutureOr<core::int?>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L17:
        {}
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function returnAsync5() → asy::Future<Null> /* originally async */ {
    final asy::_Future<Null> :async_future = new asy::_Future::•<Null>();
    core::bool* :is_sync = false;
    FutureOr<Null>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L18:
        {}
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function returnAsync6() → asy::Future<core::int?> /* originally async */ {
    final asy::_Future<core::int?> :async_future = new asy::_Future::•<core::int?>();
    core::bool* :is_sync = false;
    FutureOr<core::int?>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L19:
        {
          :return_value = null;
          break #L19;
        }
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function returnAsync7() → asy::Future<core::int?> /* originally async */ {
    final asy::_Future<core::int?> :async_future = new asy::_Future::•<core::int?>();
    core::bool* :is_sync = false;
    FutureOr<core::int?>? :return_value;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try {
        #L20:
        {}
        asy::_completeOnAsyncReturn(:async_future, :return_value, :is_sync);
        return;
      }
      on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
        asy::_completeOnAsyncError(:async_future, exception, stack_trace, :is_sync);
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :async_op.call();
    :is_sync = true;
    return :async_future;
  }
  function yieldSync() → core::Iterable<dynamic> /* originally sync* */ {
    function :sync_op_gen() → (core::_SyncIterator<dynamic>?, dynamic, dynamic) → core::bool* {
      core::int :await_jump_var = 0;
      dynamic :await_ctx_var;
      function :sync_op(core::_SyncIterator<dynamic>? :iterator, dynamic :exception, dynamic :stack_trace) → core::bool* yielding {
        {}
        return false;
      }
      return :sync_op;
    }
    return new core::_SyncIterable::•<dynamic>(:sync_op_gen);
  }
  function yieldAsync() → asy::Stream<dynamic> /* originally async* */ {
    asy::_AsyncStarStreamController<dynamic>? :controller;
    dynamic :controller_stream;
    (dynamic) → dynamic :async_op_then;
    (core::Object, core::StackTrace) → dynamic :async_op_error;
    core::int :await_jump_var = 0;
    dynamic :await_ctx_var;
    function :async_op([dynamic :result, dynamic :exception, dynamic :stack_trace]) → dynamic yielding 
      try
        try {
          #L21:
          {}
          return;
        }
        on dynamic catch(dynamic exception, core::StackTrace stack_trace) {
          :controller.{asy::_AsyncStarStreamController::addError}(exception, stack_trace);
        }
      finally {
        :controller.{asy::_AsyncStarStreamController::close}();
      }
    :async_op_then = asy::_asyncThenWrapperHelper(:async_op);
    :async_op_error = asy::_asyncErrorWrapperHelper(:async_op);
    :controller = new asy::_AsyncStarStreamController::•<dynamic>(:async_op);
    :controller_stream = :controller.{asy::_AsyncStarStreamController::stream};
    return :controller_stream;
  }
  function caseReturn1(self::Enum e) → self::Enum {
    switch(e) {
      #L22:
      case #C3:
        {
          return e;
        }
      #L23:
      case #C6:
        {
          return e;
        }
      #L24:
      default:
        throw new _in::ReachabilityError::•("`null` encountered as case in a switch expression with a non-nullable enum type.");
    }
  }
  function caseReturn2(self::Enum e) → self::Enum {
    switch(e) {
      #L25:
      case #C3:
        {
          return e;
        }
      #L26:
      default:
        {}
    }
    return let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/return_null.dart:108:3: Error: A non-null value must be returned since the return type 'Enum' doesn't allow null.
 - 'Enum' is from 'pkg/front_end/testcases/nnbd/return_null.dart'.
  Enum caseReturn2(Enum e) /* error */ {
  ^" in null;
  }
  core::bool b = false;
  core::int? local1 = (() → core::int? {
    if(b)
      return 0;
  }).call();
  core::int? local2 = (() → core::int? {
    if(b)
      return null;
    if(!b)
      return 0;
  }).call();
}
static method main() → dynamic {}

constants  {
  #C1 = 0
  #C2 = "Enum.a"
  #C3 = self::Enum {index:#C1, _name:#C2}
  #C4 = 1
  #C5 = "Enum.b"
  #C6 = self::Enum {index:#C4, _name:#C5}
  #C7 = <self::Enum*>[#C3, #C6]
}


Constructor coverage from constants:
org-dartlang-testcase:///return_null.dart:
- Enum. (from org-dartlang-testcase:///return_null.dart:43:6)
- Object. (from org-dartlang-sdk:///sdk/lib/core/object.dart:25:9)