diff --git a/lib/src/package_config.dart b/lib/src/package_config.dart
index fad20f7..0493dcc 100644
--- a/lib/src/package_config.dart
+++ b/lib/src/package_config.dart
@@ -2,10 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.10
-
-import 'package:meta/meta.dart';
-
 import 'package:pub_semver/pub_semver.dart';
 
 import 'language_version.dart';
@@ -22,38 +18,36 @@
 
   /// Date-time the `.dart_tool/package_config.json` file was generated.
   ///
-  /// This property is **optional** and may be `null` if not given.
-  DateTime generated;
+  /// `null` if not given.
+  DateTime? generated;
 
   /// Tool that generated the `.dart_tool/package_config.json` file.
   ///
   /// For `pub` this is always `'pub'`.
   ///
-  /// This property is **optional** and may be `null` if not given.
-  String generator;
+  /// `null` if not given.
+  String? generator;
 
   /// Version of the tool that generated the `.dart_tool/package_config.json`
   /// file.
   ///
   /// For `pub` this is the Dart SDK version from which `pub get` was called.
   ///
-  /// This property is **optional** and may be `null` if not given.
-  Version generatorVersion;
+  /// `null` if not given.
+  Version? generatorVersion;
 
   /// Additional properties not in the specification for the
   /// `.dart_tool/package_config.json` file.
   Map<String, dynamic> additionalProperties;
 
   PackageConfig({
-    @required this.configVersion,
-    @required this.packages,
+    required this.configVersion,
+    required this.packages,
     this.generated,
     this.generator,
     this.generatorVersion,
-    this.additionalProperties,
-  }) {
-    additionalProperties ??= {};
-  }
+    Map<String, dynamic>? additionalProperties,
+  }) : additionalProperties = additionalProperties ?? {};
 
   /// Create [PackageConfig] from JSON [data].
   ///
@@ -63,7 +57,7 @@
     if (data is! Map<String, dynamic>) {
       throw FormatException('package_config.json must be a JSON object');
     }
-    final root = data as Map<String, dynamic>;
+    final root = data;
 
     void _throw(String property, String mustBe) => throw FormatException(
         '"$property" in .dart_tool/package_config.json $mustBe');
@@ -87,7 +81,7 @@
     }
 
     // Read the 'generated' property
-    DateTime generated;
+    DateTime? generated;
     final generatedRaw = root['generated'];
     if (generatedRaw != null) {
       if (generatedRaw is! String) {
@@ -104,7 +98,7 @@
     }
 
     // Read the 'generatorVersion' property
-    Version generatorVersion;
+    Version? generatorVersion;
     final generatorVersionRaw = root['generatorVersion'];
     if (generatorVersionRaw != null) {
       if (generatorVersionRaw is! String) {
@@ -134,13 +128,13 @@
   }
 
   /// Convert to JSON structure.
-  Map<String, Object> toJson() => {
+  Map<String, Object?> toJson() => {
         'configVersion': configVersion,
         'packages': packages.map((p) => p.toJson()).toList(),
-        'generated': generated?.toUtc()?.toIso8601String(),
+        'generated': generated?.toUtc().toIso8601String(),
         'generator': generator,
         'generatorVersion': generatorVersion?.toString(),
-      }..addAll(additionalProperties ?? {});
+      }..addAll(additionalProperties);
 }
 
 class PackageConfigEntry {
@@ -158,8 +152,8 @@
   /// Import statements in Dart programs are resolved relative to this folder.
   /// This must be in the sub-tree under [rootUri].
   ///
-  /// This property is **optional** and may be `null` if not given.
-  Uri packageUri;
+  /// `null` if not given.
+  Uri? packageUri;
 
   /// Language version used by package.
   ///
@@ -167,16 +161,16 @@
   /// comment. This is derived from the lower-bound on the Dart SDK requirement
   /// in the `pubspec.yaml` for the given package.
   ///
-  /// This property is **optional** and may be `null` if not given.
-  LanguageVersion languageVersion;
+  /// `null` if not given.
+  LanguageVersion? languageVersion;
 
   /// Additional properties not in the specification for the
   /// `.dart_tool/package_config.json` file.
-  Map<String, dynamic> additionalProperties;
+  Map<String, dynamic>? additionalProperties;
 
   PackageConfigEntry({
-    @required this.name,
-    @required this.rootUri,
+    required this.name,
+    required this.rootUri,
     this.packageUri,
     this.languageVersion,
     this.additionalProperties,
@@ -193,9 +187,9 @@
       throw FormatException(
           'packages[] entries in package_config.json must be JSON objects');
     }
-    final root = data as Map<String, dynamic>;
+    final root = data;
 
-    void _throw(String property, String mustBe) => throw FormatException(
+    Never _throw(String property, String mustBe) => throw FormatException(
         '"packages[].$property" in .dart_tool/package_config.json $mustBe');
 
     final name = root['name'];
@@ -203,7 +197,7 @@
       _throw('name', 'must be a string');
     }
 
-    Uri rootUri;
+    final Uri rootUri;
     final rootUriRaw = root['rootUri'];
     if (rootUriRaw is! String) {
       _throw('rootUri', 'must be a string');
@@ -214,7 +208,7 @@
       _throw('rootUri', 'must be a URI');
     }
 
-    Uri packageUri;
+    Uri? packageUri;
     var packageUriRaw = root['packageUri'];
     if (packageUriRaw != null) {
       if (packageUriRaw is! String) {
@@ -230,7 +224,7 @@
       }
     }
 
-    LanguageVersion languageVersion;
+    LanguageVersion? languageVersion;
     final languageVersionRaw = root['languageVersion'];
     if (languageVersionRaw != null) {
       if (languageVersionRaw is! String) {
@@ -252,7 +246,7 @@
   }
 
   /// Convert to JSON structure.
-  Map<String, Object> toJson() => {
+  Map<String, Object?> toJson() => {
         'name': name,
         'rootUri': rootUri.toString(),
         if (packageUri != null) 'packageUri': packageUri?.toString(),
diff --git a/lib/src/rate_limited_scheduler.dart b/lib/src/rate_limited_scheduler.dart
index 6e62310..daeb76f 100644
--- a/lib/src/rate_limited_scheduler.dart
+++ b/lib/src/rate_limited_scheduler.dart
@@ -2,12 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.10
-
 import 'dart:async';
 import 'dart:collection';
 
-import 'package:meta/meta.dart';
 import 'package:pedantic/pedantic.dart';
 import 'package:pool/pool.dart';
 
@@ -65,7 +62,7 @@
   final Set<J> _started = {};
 
   RateLimitedScheduler(Future<V> Function(J) runJob,
-      {@required int maxConcurrentOperations})
+      {required int maxConcurrentOperations})
       : _runJob = runJob,
         _pool = Pool(maxConcurrentOperations);
 
@@ -77,7 +74,7 @@
       return;
     }
     final task = _queue.removeFirst();
-    final completer = _cache[task.jobId];
+    final completer = _cache[task.jobId]!;
 
     if (!_started.add(task.jobId)) {
       return;
@@ -140,7 +137,7 @@
 
   /// Returns the result of running [jobId] if that is already done.
   /// Otherwise returns `null`.
-  V peek(J jobId) => _results[jobId];
+  V? peek(J jobId) => _results[jobId];
 }
 
 class _Task<J> {
diff --git a/tool/test.dart b/tool/test.dart
index 2f4769d..e7877a2 100755
--- a/tool/test.dart
+++ b/tool/test.dart
@@ -3,8 +3,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart=2.10
-
 /// Test wrapper script.
 /// Many of the integration tests runs the `pub` command, this is slow if every
 /// invocation requires the dart compiler to load all the sources. This script
@@ -19,7 +17,7 @@
 import 'package:pub/src/exceptions.dart';
 
 Future<void> main(List<String> args) async {
-  Process testProcess;
+  Process? testProcess;
   final sub = ProcessSignal.sigint.watch().listen((signal) {
     testProcess?.kill(signal);
   });