diff --git a/packages/flutter_web_plugins/lib/flutter_web_plugins.dart b/packages/flutter_web_plugins/lib/flutter_web_plugins.dart
index 1bb8281b871..53a19bdbabd 100644
--- a/packages/flutter_web_plugins/lib/flutter_web_plugins.dart
+++ b/packages/flutter_web_plugins/lib/flutter_web_plugins.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 /// The platform channels and plugin registry implementations for
 /// the web implementations of Flutter plugins.
 ///
diff --git a/packages/flutter_web_plugins/lib/src/navigation/js_url_strategy.dart b/packages/flutter_web_plugins/lib/src/navigation/js_url_strategy.dart
index 9ebaac560e7..86621eb3909 100644
--- a/packages/flutter_web_plugins/lib/src/navigation/js_url_strategy.dart
+++ b/packages/flutter_web_plugins/lib/src/navigation/js_url_strategy.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @JS()
 library js_location_strategy;
 
@@ -16,7 +14,7 @@ import 'package:meta/meta.dart';
 
 import 'url_strategy.dart';
 
-typedef _JsSetUrlStrategy = void Function(JsUrlStrategy);
+typedef _JsSetUrlStrategy = void Function(JsUrlStrategy?);
 
 /// A JavaScript hook to customize the URL strategy of a Flutter app.
 //
@@ -29,7 +27,7 @@ external _JsSetUrlStrategy get jsSetUrlStrategy;
 
 typedef _PathGetter = String Function();
 
-typedef _StateGetter = Object Function();
+typedef _StateGetter = Object? Function();
 
 typedef _AddPopStateListener = ui.VoidCallback Function(html.EventListener);
 
@@ -43,10 +41,6 @@ typedef _HistoryMove = Future<void> Function(int count);
 /// Given a Dart implementation of URL strategy, converts it to a JavaScript
 /// URL strategy to be passed through JS interop.
 JsUrlStrategy convertToJsUrlStrategy(UrlStrategy strategy) {
-  if (strategy == null) {
-    return null;
-  }
-
   return JsUrlStrategy(
     getPath: allowInterop(strategy.getPath),
     getState: allowInterop(strategy.getState),
diff --git a/packages/flutter_web_plugins/lib/src/navigation/url_strategy.dart b/packages/flutter_web_plugins/lib/src/navigation/url_strategy.dart
index 2470f6bf0e4..59360cb5956 100644
--- a/packages/flutter_web_plugins/lib/src/navigation/url_strategy.dart
+++ b/packages/flutter_web_plugins/lib/src/navigation/url_strategy.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:html' as html;
 import 'dart:ui' as ui;
@@ -14,8 +12,12 @@ import 'utils.dart';
 /// Change the strategy to use for handling browser URL.
 ///
 /// Setting this to null disables all integration with the browser history.
-void setUrlStrategy(UrlStrategy strategy) {
-  jsSetUrlStrategy(convertToJsUrlStrategy(strategy));
+void setUrlStrategy(UrlStrategy? strategy) {
+  JsUrlStrategy? jsUrlStrategy;
+  if (strategy != null) {
+    jsUrlStrategy = convertToJsUrlStrategy(strategy);
+  }
+  jsSetUrlStrategy(jsUrlStrategy);
 }
 
 /// Represents and reads route state from the browser's URL.
@@ -37,7 +39,7 @@ abstract class UrlStrategy {
   /// The state of the current browser history entry.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/History/state
-  Object getState();
+  Object? getState();
 
   /// Given a path that's internal to the app, create the external url that
   /// will be used in the browser.
@@ -101,7 +103,7 @@ class HashUrlStrategy extends UrlStrategy {
   String getPath() {
     // the hash value is always prefixed with a `#`
     // and if it is empty then it will stay empty
-    final String path = _platformLocation.hash ?? '';
+    final String path = _platformLocation.hash;
     assert(path.isEmpty || path.startsWith('#'));
 
     // We don't want to return an empty string as a path. Instead we default to "/".
@@ -113,7 +115,7 @@ class HashUrlStrategy extends UrlStrategy {
   }
 
   @override
-  Object getState() => _platformLocation.state;
+  Object? getState() => _platformLocation.state;
 
   @override
   String prepareExternalUrl(String internalUrl) {
@@ -148,7 +150,7 @@ class HashUrlStrategy extends UrlStrategy {
   /// `history.back` transition.
   Future<void> _waitForPopState() {
     final Completer<void> completer = Completer<void>();
-    ui.VoidCallback unsubscribe;
+    late ui.VoidCallback unsubscribe;
     unsubscribe = addPopStateListener((_) {
       unsubscribe();
       completer.complete();
@@ -238,7 +240,7 @@ abstract class PlatformLocation {
   /// The `state` in the current history entry.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/API/History/state
-  Object get state;
+  Object? get state;
 
   /// Adds a new entry to the browser history stack.
   ///
@@ -266,7 +268,7 @@ abstract class PlatformLocation {
   /// The base href where the Flutter app is being served.
   ///
   /// See: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
-  String getBaseHref();
+  String? getBaseHref();
 }
 
 /// Delegates to real browser APIs to provide platform location functionality.
@@ -274,6 +276,14 @@ class BrowserPlatformLocation extends PlatformLocation {
   /// Default constructor for [BrowserPlatformLocation].
   const BrowserPlatformLocation();
 
+  // Default value for [pathname] when it's not set in window.location.
+  // According to MDN this should be ''. Chrome seems to return '/'.
+  static const String _defaultPathname = '';
+
+  // Default value for [search] when it's not set in window.location.
+  // According to both chrome, and the MDN, this is ''.
+  static const String _defaultSearch = '';
+
   html.Location get _location => html.window.location;
   html.History get _history => html.window.history;
 
@@ -288,16 +298,16 @@ class BrowserPlatformLocation extends PlatformLocation {
   }
 
   @override
-  String get pathname => _location.pathname;
+  String get pathname => _location.pathname ?? _defaultPathname;
 
   @override
-  String get search => _location.search;
+  String get search => _location.search ?? _defaultSearch;
 
   @override
   String get hash => _location.hash;
 
   @override
-  Object get state => _history.state;
+  Object? get state => _history.state;
 
   @override
   void pushState(Object state, String title, String url) {
@@ -315,6 +325,5 @@ class BrowserPlatformLocation extends PlatformLocation {
   }
 
   @override
-  String getBaseHref() => getBaseElementHrefFromDom();
-  // String getBaseHref() => html.document.baseUri;
+  String? getBaseHref() => getBaseElementHrefFromDom();
 }
diff --git a/packages/flutter_web_plugins/lib/src/navigation/utils.dart b/packages/flutter_web_plugins/lib/src/navigation/utils.dart
index ea742aa8e7d..a1250cdd25a 100644
--- a/packages/flutter_web_plugins/lib/src/navigation/utils.dart
+++ b/packages/flutter_web_plugins/lib/src/navigation/utils.dart
@@ -2,43 +2,33 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:html';
 
-AnchorElement _urlParsingNode;
+// TODO(mdebbar): Use the `URI` class instead?
+final AnchorElement _urlParsingNode = AnchorElement();
 
 /// Extracts the pathname part of a full [url].
 ///
 /// Example: for the url `http://example.com/foo`, the extracted pathname will
 /// be `/foo`.
 String extractPathname(String url) {
-  // TODO(mdebbar): Use the `URI` class instead?
-  _urlParsingNode ??= AnchorElement();
   _urlParsingNode.href = url;
-  final String pathname = _urlParsingNode.pathname;
+  final String pathname = _urlParsingNode.pathname ?? '';
   return (pathname.isEmpty || pathname[0] == '/') ? pathname : '/$pathname';
 }
 
-Element _baseElement;
+// The <base> element in the document.
+final Element? _baseElement = document.querySelector('base');
 
-/// Finds the <base> element in the document and returns its `href` attribute.
+/// Returns the `href` attribute of the <base> element in the document.
 ///
 /// Returns null if the element isn't found.
-String getBaseElementHrefFromDom() {
-  if (_baseElement == null) {
-    _baseElement = document.querySelector('base');
-    if (_baseElement == null) {
-      return null;
-    }
-  }
-  return _baseElement.getAttribute('href');
-}
+String? getBaseElementHrefFromDom() => _baseElement?.getAttribute('href');
 
 /// Checks that [baseHref] is set.
 ///
 /// Throws an exception otherwise.
-String checkBaseHref(String baseHref) {
+String checkBaseHref(String? baseHref) {
   if (baseHref == null) {
     throw Exception('Please add a <base> element to your index.html');
   }
diff --git a/packages/flutter_web_plugins/lib/src/plugin_event_channel.dart b/packages/flutter_web_plugins/lib/src/plugin_event_channel.dart
index eea612e1d73..d84f36190b6 100644
--- a/packages/flutter_web_plugins/lib/src/plugin_event_channel.dart
+++ b/packages/flutter_web_plugins/lib/src/plugin_event_channel.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:flutter/services.dart';
@@ -28,14 +26,14 @@ import 'plugin_registry.dart';
 ///
 /// The first method is `listen`. When called, it begins forwarding
 /// messages to the framework side when they are added to the
-/// [controller]. This triggers the [StreamController.onListen] callback
-/// on the [controller].
+/// `controller`. This triggers the [StreamController.onListen] callback
+/// on the `controller`.
 ///
 /// The other method is `cancel`. When called, it stops forwarding
 /// events to the framework. This triggers the [StreamController.onCancel]
-/// callback on the [controller].
+/// callback on the `controller`.
 ///
-/// Events added to the [controller] when the framework is not
+/// Events added to the `controller` when the framework is not
 /// subscribed are silently discarded.
 class PluginEventChannel<T> {
   /// Creates a new plugin event channel.
@@ -45,8 +43,8 @@ class PluginEventChannel<T> {
     this.name, [
     this.codec = const StandardMethodCodec(),
     this.binaryMessenger,
-  ])  : assert(name != null),
-        assert(codec != null);
+  ]) : assert(name != null), // ignore: unnecessary_null_comparison
+       assert(codec != null); // ignore: unnecessary_null_comparison
 
   /// The logical channel on which communication happens.
   ///
@@ -63,7 +61,7 @@ class PluginEventChannel<T> {
   /// When this is null, the [pluginBinaryMessenger] is used instead,
   /// which sends messages from the platform-side to the
   /// framework-side.
-  final BinaryMessenger binaryMessenger;
+  final BinaryMessenger? binaryMessenger;
 
   /// Use [setController] instead.
   ///
@@ -81,7 +79,7 @@ class PluginEventChannel<T> {
   ///
   /// Setting the controller to null disconnects from the channel (setting
   /// the message handler on the [binaryMessenger] to null).
-  void setController(StreamController<T> controller) {
+  void setController(StreamController<T>? controller) {
     final BinaryMessenger messenger = binaryMessenger ?? pluginBinaryMessenger;
     if (controller == null) {
       messenger.setMessageHandler(name, null);
@@ -105,16 +103,21 @@ class PluginEventChannel<T> {
 }
 
 class _EventChannelHandler<T> {
-  _EventChannelHandler(this.name, this.codec, this.controller, this.messenger) : assert(messenger != null);
+  _EventChannelHandler(
+    this.name,
+    this.codec,
+    this.controller,
+    this.messenger,
+  ) : assert(messenger != null); // ignore: unnecessary_null_comparison
 
   final String name;
   final MethodCodec codec;
   final StreamController<T> controller;
   final BinaryMessenger messenger;
 
-  StreamSubscription<T> subscription;
+  StreamSubscription<T>? subscription;
 
-  Future<ByteData> handle(ByteData message) {
+  Future<ByteData>? handle(ByteData? message) {
     final MethodCall call = codec.decodeMethodCall(message);
     switch (call.method) {
       case 'listen':
@@ -128,9 +131,8 @@ class _EventChannelHandler<T> {
   }
 
   Future<ByteData> _listen() async {
-    if (subscription != null) {
-      await subscription.cancel();
-    }
+    // Cancel any existing subscription.
+    await subscription?.cancel();
     subscription = controller.stream.listen((dynamic event) {
       messenger.send(name, codec.encodeSuccessEnvelope(event));
     }, onError: (dynamic error) {
@@ -146,7 +148,7 @@ class _EventChannelHandler<T> {
         message: 'No active subscription to cancel.',
       );
     }
-    await subscription.cancel();
+    await subscription!.cancel();
     subscription = null;
     return codec.encodeSuccessEnvelope(null);
   }
diff --git a/packages/flutter_web_plugins/lib/src/plugin_registry.dart b/packages/flutter_web_plugins/lib/src/plugin_registry.dart
index 9563ea97cd9..f9a2fff6a4f 100644
--- a/packages/flutter_web_plugins/lib/src/plugin_registry.dart
+++ b/packages/flutter_web_plugins/lib/src/plugin_registry.dart
@@ -2,15 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
-typedef _MessageHandler = Future<ByteData> Function(ByteData);
+// TODO(hterkelsen): Why is this _MessageHandler duplicated here?
+typedef _MessageHandler = Future<ByteData?>? Function(ByteData?);
 
 /// This class registers web platform plugins.
 ///
@@ -97,12 +96,12 @@ class _PlatformBinaryMessenger extends BinaryMessenger {
   @override
   Future<void> handlePlatformMessage(
     String channel,
-    ByteData data,
-    ui.PlatformMessageResponseCallback callback,
+    ByteData? data,
+    ui.PlatformMessageResponseCallback? callback,
   ) async {
-    ByteData response;
+    ByteData? response;
     try {
-      final MessageHandler handler = _handlers[channel];
+      final MessageHandler? handler = _handlers[channel];
       if (handler != null) {
         response = await handler(data);
       }
@@ -122,9 +121,9 @@ class _PlatformBinaryMessenger extends BinaryMessenger {
 
   /// Sends a platform message from the platform side back to the framework.
   @override
-  Future<ByteData> send(String channel, ByteData message) {
+  Future<ByteData> send(String channel, ByteData? message) {
     final Completer<ByteData> completer = Completer<ByteData>();
-    ui.window.onPlatformMessage(channel, message, (ByteData reply) {
+    ui.window.onPlatformMessage!(channel, message, (ByteData? reply) {
       try {
         completer.complete(reply);
       } catch (exception, stack) {
@@ -140,7 +139,7 @@ class _PlatformBinaryMessenger extends BinaryMessenger {
   }
 
   @override
-  void setMessageHandler(String channel, MessageHandler handler) {
+  void setMessageHandler(String channel, MessageHandler? handler) {
     if (handler == null)
       _handlers.remove(channel);
     else
@@ -148,12 +147,12 @@ class _PlatformBinaryMessenger extends BinaryMessenger {
   }
 
   @override
-  bool checkMessageHandler(String channel, MessageHandler handler) => _handlers[channel] == handler;
+  bool checkMessageHandler(String channel, MessageHandler? handler) => _handlers[channel] == handler;
 
   @override
   void setMockMessageHandler(
     String channel,
-    Future<ByteData> Function(ByteData message) handler,
+    MessageHandler? handler,
   ) {
     throw FlutterError(
       'Setting mock handlers is not supported on the platform side.',
@@ -161,7 +160,7 @@ class _PlatformBinaryMessenger extends BinaryMessenger {
   }
 
   @override
-  bool checkMockMessageHandler(String channel, MessageHandler handler) {
+  bool checkMockMessageHandler(String channel, MessageHandler? handler) {
     throw FlutterError(
       'Setting mock handlers is not supported on the platform side.',
     );
diff --git a/packages/flutter_web_plugins/pubspec.yaml b/packages/flutter_web_plugins/pubspec.yaml
index b4550801199..e0f19e5dc60 100644
--- a/packages/flutter_web_plugins/pubspec.yaml
+++ b/packages/flutter_web_plugins/pubspec.yaml
@@ -4,7 +4,7 @@ author: Flutter Authors <flutter-dev@googlegroups.com>
 homepage: http://flutter.dev
 
 environment:
-  sdk: ">=2.0.0-dev.28.0 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   flutter:
diff --git a/packages/flutter_web_plugins/test/navigation/url_strategy_test.dart b/packages/flutter_web_plugins/test/navigation/url_strategy_test.dart
index 156a631aa40..b3f9de79cd9 100644
--- a/packages/flutter_web_plugins/test/navigation/url_strategy_test.dart
+++ b/packages/flutter_web_plugins/test/navigation/url_strategy_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:html';
 
 @TestOn('chrome') // Uses web-only Flutter SDK
@@ -13,16 +11,12 @@ import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 
 void main() {
   group('$HashUrlStrategy', () {
-    TestPlatformLocation location;
+    late TestPlatformLocation location;
 
     setUp(() {
       location = TestPlatformLocation();
     });
 
-    tearDown(() {
-      location = null;
-    });
-
     test('leading slash is optional', () {
       final HashUrlStrategy strategy = HashUrlStrategy(location);
 
@@ -48,16 +42,12 @@ void main() {
   });
 
   group('$PathUrlStrategy', () {
-    TestPlatformLocation location;
+    late TestPlatformLocation location;
 
     setUp(() {
       location = TestPlatformLocation();
     });
 
-    tearDown(() {
-      location = null;
-    });
-
     test('validates base href', () {
       location.baseHref = '/';
       expect(
@@ -153,7 +143,7 @@ class TestPlatformLocation extends PlatformLocation {
   String hash = '';
 
   @override
-  dynamic state;
+  Object? Function() state = () => null;
 
   /// Mocks the base href of the document.
   String baseHref = '';
diff --git a/packages/flutter_web_plugins/test/navigation/utils_test.dart b/packages/flutter_web_plugins/test/navigation/utils_test.dart
index 419b49f7f64..fa834809947 100644
--- a/packages/flutter_web_plugins/test/navigation/utils_test.dart
+++ b/packages/flutter_web_plugins/test/navigation/utils_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @TestOn('browser') // Uses web-only Flutter SDK
 
 import 'package:flutter_test/flutter_test.dart';
diff --git a/packages/flutter_web_plugins/test/plugin_event_channel_test.dart b/packages/flutter_web_plugins/test/plugin_event_channel_test.dart
index e7a1a8502e7..fcac25a290b 100644
--- a/packages/flutter_web_plugins/test/plugin_event_channel_test.dart
+++ b/packages/flutter_web_plugins/test/plugin_event_channel_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @TestOn('chrome') // Uses web-only Flutter SDK
 
 import 'dart:async';
@@ -29,7 +27,7 @@ void main() {
           PluginEventChannel<String>('test');
 
       final StreamController<String> controller = StreamController<String>();
-      sendingChannel.controller = controller;
+      sendingChannel.setController(controller);
 
       expect(listeningChannel.receiveBroadcastStream(),
           emitsInOrder(<String>['hello', 'world']));
@@ -61,7 +59,7 @@ void main() {
           PluginEventChannel<String>('test2');
 
       final StreamController<String> controller = StreamController<String>();
-      sendingChannel.controller = controller;
+      sendingChannel.setController(controller);
 
       expect(
           listeningChannel.receiveBroadcastStream(),
@@ -96,7 +94,7 @@ void main() {
 
       final StreamController<String> controller = StreamController<String>(
           onListen: expectAsync0<void>(() {}, count: 1));
-      sendingChannel.controller = controller;
+      sendingChannel.setController(controller);
 
       expect(listeningChannel.receiveBroadcastStream(),
           emitsInOrder(<String>['hello']));
@@ -128,11 +126,11 @@ void main() {
 
       final StreamController<String> controller =
           StreamController<String>(onCancel: expectAsync0<void>(() {}));
-      sendingChannel.controller = controller;
+      sendingChannel.setController(controller);
 
       final Stream<dynamic> eventStream =
           listeningChannel.receiveBroadcastStream();
-      StreamSubscription<dynamic> subscription;
+      late StreamSubscription<dynamic> subscription;
       subscription =
           eventStream.listen(expectAsync1<void, dynamic>((dynamic x) {
         expect(x, equals('hello'));
@@ -153,7 +151,7 @@ void main() {
 
       final Stream<dynamic> eventStream =
           listeningChannel.receiveBroadcastStream();
-      StreamSubscription<dynamic> subscription;
+      late StreamSubscription<dynamic> subscription;
       subscription =
           eventStream.listen(expectAsync1<void, dynamic>((dynamic x) {
         expect(x, equals('hello'));
diff --git a/packages/flutter_web_plugins/test/plugin_registry_test.dart b/packages/flutter_web_plugins/test/plugin_registry_test.dart
index 64464a5e3f5..79571000fc0 100644
--- a/packages/flutter_web_plugins/test/plugin_registry_test.dart
+++ b/packages/flutter_web_plugins/test/plugin_registry_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 @TestOn('chrome') // Uses web-only Flutter SDK
 
 import 'dart:ui' as ui; // ignore: unused_import, it looks unused as web-only elements are the only elements used.
@@ -56,8 +54,8 @@ void main() {
       const StandardMessageCodec codec = StandardMessageCodec();
 
       final List<String> loggedMessages = <String>[];
-      ServicesBinding.instance.defaultBinaryMessenger
-          .setMessageHandler('test_send', (ByteData data) {
+      ServicesBinding.instance!.defaultBinaryMessenger
+          .setMessageHandler('test_send', (ByteData? data) {
         loggedMessages.add(codec.decodeMessage(data) as String);
         return null;
       });
@@ -70,14 +68,14 @@ void main() {
           'test_send', codec.encodeMessage('world'));
       expect(loggedMessages, equals(<String>['hello', 'world']));
 
-      ServicesBinding.instance.defaultBinaryMessenger
+      ServicesBinding.instance!.defaultBinaryMessenger
           .setMessageHandler('test_send', null);
     });
 
     test('throws when trying to set a mock handler', () {
       expect(
           () => pluginBinaryMessenger.setMockMessageHandler(
-              'test', (ByteData data) async => ByteData(0)),
+              'test', (ByteData? data) async => ByteData(0)),
           throwsFlutterError);
     });
   });