diff --git a/analysis_options.yaml b/analysis_options.yaml
index c61a77070..5bc20088b 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -12,7 +12,12 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 
-include: package:pedantic/analysis_options.1.8.0.yaml
+include: package:pedantic/analysis_options.1.11.0.yaml
+
+analyzer:
+  errors:
+    omit_local_variable_types: ignore
+
 linter:
   rules:
     - public_member_api_docs
diff --git a/packages/google_mobile_ads/CHANGELOG.md b/packages/google_mobile_ads/CHANGELOG.md
index 2751c6cbb..9658a3604 100644
--- a/packages/google_mobile_ads/CHANGELOG.md
+++ b/packages/google_mobile_ads/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 0.12.0
+
+* Migrated to null safety. Minimum Dart SDK version is bumped to 2.12.0.
+
 ## 0.11.0+4
 
 * Fixes a [bug](https://github.com/googleads/googleads-mobile-flutter/issues/47) where state is not properly cleaned up on hot restart.
diff --git a/packages/google_mobile_ads/android/src/main/java/io/flutter/plugins/googlemobileads/Constants.java b/packages/google_mobile_ads/android/src/main/java/io/flutter/plugins/googlemobileads/Constants.java
index c28d9bae0..f3a3dccd3 100644
--- a/packages/google_mobile_ads/android/src/main/java/io/flutter/plugins/googlemobileads/Constants.java
+++ b/packages/google_mobile_ads/android/src/main/java/io/flutter/plugins/googlemobileads/Constants.java
@@ -17,5 +17,5 @@
 /** Constants used in the plugin. */
 public class Constants {
   /** Version request agent. Should be bumped alongside plugin versions. */
-  public static final String REQUEST_AGENT_PREFIX_VERSIONED = "Flutter-GMA-0.11.0+4";
+  public static final String REQUEST_AGENT_PREFIX_VERSIONED = "Flutter-GMA-0.12.0";
 }
diff --git a/packages/google_mobile_ads/example/analysis_options.yaml b/packages/google_mobile_ads/example/analysis_options.yaml
new file mode 100644
index 000000000..9b541d2af
--- /dev/null
+++ b/packages/google_mobile_ads/example/analysis_options.yaml
@@ -0,0 +1,15 @@
+#  Copyright 2021 Google LLC
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#  https://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+include: ../../../analysis_options.yaml
diff --git a/packages/google_mobile_ads/example/lib/main.dart b/packages/google_mobile_ads/example/lib/main.dart
index b5253c4fd..e9f39ae5e 100644
--- a/packages/google_mobile_ads/example/lib/main.dart
+++ b/packages/google_mobile_ads/example/lib/main.dart
@@ -33,16 +33,16 @@ class MyApp extends StatefulWidget {
 
 class _MyAppState extends State<MyApp> {
   static final AdRequest request = AdRequest(
-    testDevices: testDevice != null ? <String>[testDevice] : null,
+    testDevices: <String>[testDevice],
     keywords: <String>['foo', 'bar'],
     contentUrl: 'http://foo.com/bar.html',
     nonPersonalizedAds: true,
   );
 
-  InterstitialAd _interstitialAd;
+  InterstitialAd? _interstitialAd;
   bool _interstitialReady = false;
 
-  RewardedAd _rewardedAd;
+  RewardedAd? _rewardedAd;
   bool _rewardedReady = false;
 
   @override
@@ -54,7 +54,7 @@ class _MyAppState extends State<MyApp> {
           .updateRequestConfiguration(RequestConfiguration(
               tagForChildDirectedTreatment:
                   TagForChildDirectedTreatment.unspecified))
-          .then((value) {
+          .then((void value) {
         createInterstitialAd();
         createRewardedAd();
       });
@@ -130,7 +130,7 @@ class _MyAppState extends State<MyApp> {
   Widget build(BuildContext context) {
     return MaterialApp(
       home: Builder(
-        builder: (context) => Scaffold(
+        builder: (BuildContext context) => Scaffold(
           appBar: AppBar(
             title: const Text('AdMob Plugin example app'),
             actions: <Widget>[
@@ -139,39 +139,40 @@ class _MyAppState extends State<MyApp> {
                   switch (result) {
                     case 'InterstitialAd':
                       if (!_interstitialReady) return;
-                      _interstitialAd.show();
+                      _interstitialAd!.show();
                       _interstitialReady = false;
                       _interstitialAd = null;
                       break;
                     case 'RewardedAd':
                       if (!_rewardedReady) return;
-                      _rewardedAd.show();
+                      _rewardedAd!.show();
                       _rewardedReady = false;
                       _rewardedAd = null;
                       break;
                     case 'ReusableInlineExample':
                       Navigator.push(
                         context,
-                        MaterialPageRoute(
-                            builder: (context) => ReusableInlineExample()),
+                        MaterialPageRoute<void>(
+                            builder: (BuildContext context) =>
+                                ReusableInlineExample()),
                       );
                       break;
                     default:
-                      throw AssertionError('unexpected button: ${result}');
+                      throw AssertionError('unexpected button: $result');
                   }
                 },
                 itemBuilder: (BuildContext context) => <PopupMenuEntry<String>>[
                   PopupMenuItem<String>(
-                    child: Text('$InterstitialAd'),
                     value: '$InterstitialAd',
+                    child: Text('$InterstitialAd'),
                   ),
                   PopupMenuItem<String>(
-                    child: Text('$RewardedAd'),
                     value: '$RewardedAd',
+                    child: Text('$RewardedAd'),
                   ),
                   PopupMenuItem<String>(
-                    child: Text('Reusable Inline Ads Object Example'),
                     value: 'ReusableInlineExample',
+                    child: Text('Reusable Inline Ads Object Example'),
                   ),
                 ],
               ),
@@ -224,7 +225,7 @@ class BannerAdWidget extends StatefulWidget {
 }
 
 class BannerAdState extends State<BannerAdWidget> {
-  BannerAd _bannerAd;
+  late BannerAd _bannerAd;
   final Completer<BannerAd> bannerCompleter = Completer<BannerAd>();
 
   @override
@@ -242,21 +243,20 @@ class BannerAdState extends State<BannerAdWidget> {
         onAdFailedToLoad: (Ad ad, LoadAdError error) {
           ad.dispose();
           print('$BannerAd failedToLoad: $error');
-          bannerCompleter.completeError(null);
+          bannerCompleter.completeError(error);
         },
         onAdOpened: (Ad ad) => print('$BannerAd onAdOpened.'),
         onAdClosed: (Ad ad) => print('$BannerAd onAdClosed.'),
         onApplicationExit: (Ad ad) => print('$BannerAd onApplicationExit.'),
       ),
     );
-    Future<void>.delayed(Duration(seconds: 1), () => _bannerAd?.load());
+    Future<void>.delayed(Duration(seconds: 1), () => _bannerAd.load());
   }
 
   @override
   void dispose() {
     super.dispose();
-    _bannerAd?.dispose();
-    _bannerAd = null;
+    _bannerAd.dispose();
   }
 
   @override
@@ -283,8 +283,8 @@ class BannerAdState extends State<BannerAdWidget> {
         return Container(
           width: _bannerAd.size.width.toDouble(),
           height: _bannerAd.size.height.toDouble(),
-          child: child,
           color: Colors.blueGrey,
+          child: child,
         );
       },
     );
@@ -301,7 +301,7 @@ class PublisherBannerAdWidget extends StatefulWidget {
 }
 
 class PublisherBannerAdState extends State<PublisherBannerAdWidget> {
-  PublisherBannerAd _bannerAd;
+  late PublisherBannerAd _bannerAd;
   final Completer<PublisherBannerAd> bannerCompleter =
       Completer<PublisherBannerAd>();
 
@@ -311,7 +311,7 @@ class PublisherBannerAdState extends State<PublisherBannerAdWidget> {
     _bannerAd = PublisherBannerAd(
       adUnitId: '/6499/example/banner',
       request: PublisherAdRequest(nonPersonalizedAds: true),
-      sizes: [widget.size],
+      sizes: <AdSize>[widget.size],
       listener: AdListener(
         onAdLoaded: (Ad ad) {
           print('$PublisherBannerAd loaded.');
@@ -320,7 +320,7 @@ class PublisherBannerAdState extends State<PublisherBannerAdWidget> {
         onAdFailedToLoad: (Ad ad, LoadAdError error) {
           ad.dispose();
           print('$PublisherBannerAd failedToLoad: $error');
-          bannerCompleter.completeError(null);
+          bannerCompleter.completeError(error);
         },
         onAdOpened: (Ad ad) => print('$PublisherBannerAd onAdOpened.'),
         onAdClosed: (Ad ad) => print('$PublisherBannerAd onAdClosed.'),
@@ -328,14 +328,13 @@ class PublisherBannerAdState extends State<PublisherBannerAdWidget> {
             print('$PublisherBannerAd onApplicationExit.'),
       ),
     );
-    Future<void>.delayed(Duration(seconds: 1), () => _bannerAd?.load());
+    Future<void>.delayed(Duration(seconds: 1), () => _bannerAd.load());
   }
 
   @override
   void dispose() {
     super.dispose();
-    _bannerAd?.dispose();
-    _bannerAd = null;
+    _bannerAd.dispose();
   }
 
   @override
@@ -363,8 +362,8 @@ class PublisherBannerAdState extends State<PublisherBannerAdWidget> {
         return Container(
           width: _bannerAd.sizes[0].width.toDouble(),
           height: _bannerAd.sizes[0].height.toDouble(),
-          child: child,
           color: Colors.blueGrey,
+          child: child,
         );
       },
     );
@@ -377,7 +376,7 @@ class NativeAdWidget extends StatefulWidget {
 }
 
 class NativeAdState extends State<NativeAdWidget> {
-  NativeAd _nativeAd;
+  late NativeAd _nativeAd;
   final Completer<NativeAd> nativeAdCompleter = Completer<NativeAd>();
 
   @override
@@ -395,21 +394,20 @@ class NativeAdState extends State<NativeAdWidget> {
         onAdFailedToLoad: (Ad ad, LoadAdError error) {
           ad.dispose();
           print('$NativeAd failedToLoad: $error');
-          nativeAdCompleter.completeError(null);
+          nativeAdCompleter.completeError(error);
         },
         onAdOpened: (Ad ad) => print('$NativeAd onAdOpened.'),
         onAdClosed: (Ad ad) => print('$NativeAd onAdClosed.'),
         onApplicationExit: (Ad ad) => print('$NativeAd onApplicationExit.'),
       ),
     );
-    Future<void>.delayed(Duration(seconds: 1), () => _nativeAd?.load());
+    Future<void>.delayed(Duration(seconds: 1), () => _nativeAd.load());
   }
 
   @override
   void dispose() {
     super.dispose();
-    _nativeAd?.dispose();
-    _nativeAd = null;
+    _nativeAd.dispose();
   }
 
   @override
@@ -436,8 +434,8 @@ class NativeAdState extends State<NativeAdWidget> {
         return Container(
           width: 250,
           height: 350,
-          child: child,
           color: Colors.blueGrey,
+          child: child,
         );
       },
     );
diff --git a/packages/google_mobile_ads/example/lib/reusable_inline_example.dart b/packages/google_mobile_ads/example/lib/reusable_inline_example.dart
index d1e5a9281..aeb17cfdd 100644
--- a/packages/google_mobile_ads/example/lib/reusable_inline_example.dart
+++ b/packages/google_mobile_ads/example/lib/reusable_inline_example.dart
@@ -13,13 +13,13 @@ class ReusableInlineExample extends StatefulWidget {
 }
 
 class _ReusableInlineExampleState extends State<ReusableInlineExample> {
-  BannerAd _bannerAd;
+  BannerAd? _bannerAd;
   bool _bannerAdIsLoaded = false;
 
-  PublisherBannerAd _publisherBannerAd;
+  PublisherBannerAd? _publisherBannerAd;
   bool _publisherBannerAdIsLoaded = false;
 
-  NativeAd _nativeAd;
+  NativeAd? _nativeAd;
   bool _nativeAdIsLoaded = false;
 
   @override
@@ -39,23 +39,28 @@ class _ReusableInlineExampleState extends State<ReusableInlineExample> {
                 );
               },
               itemBuilder: (BuildContext context, int index) {
-                if (index == 5 && _bannerAdIsLoaded && _bannerAd != null) {
+                final BannerAd? bannerAd = _bannerAd;
+                if (index == 5 && _bannerAdIsLoaded && bannerAd != null) {
                   return Container(
-                      height: _bannerAd.size.height.toDouble(),
-                      width: _bannerAd.size.width.toDouble(),
-                      child: AdWidget(ad: _bannerAd));
+                      height: bannerAd.size.height.toDouble(),
+                      width: bannerAd.size.width.toDouble(),
+                      child: AdWidget(ad: bannerAd));
                 }
+
+                final PublisherBannerAd? publisherBannerAd = _publisherBannerAd;
                 if (index == 10 &&
                     _publisherBannerAdIsLoaded &&
-                    _publisherBannerAd != null) {
+                    publisherBannerAd != null) {
                   return Container(
-                      height: _publisherBannerAd.sizes[0].height.toDouble(),
-                      width: _publisherBannerAd.sizes[0].width.toDouble(),
-                      child: AdWidget(ad: _publisherBannerAd));
+                      height: publisherBannerAd.sizes[0].height.toDouble(),
+                      width: publisherBannerAd.sizes[0].width.toDouble(),
+                      child: AdWidget(ad: _publisherBannerAd!));
                 }
-                if (index == 15 && _nativeAdIsLoaded && _nativeAd != null) {
+
+                final NativeAd? nativeAd = _nativeAd;
+                if (index == 15 && _nativeAdIsLoaded && nativeAd != null) {
                   return Container(
-                      width: 250, height: 350, child: AdWidget(ad: _nativeAd));
+                      width: 250, height: 350, child: AdWidget(ad: nativeAd));
                 }
 
                 return Text(
@@ -81,7 +86,7 @@ class _ReusableInlineExampleState extends State<ReusableInlineExample> {
           onAdLoaded: (Ad ad) {
             print('$BannerAd loaded.');
             setState(() {
-              this._bannerAdIsLoaded = true;
+              _bannerAdIsLoaded = true;
             });
           },
           onAdFailedToLoad: (Ad ad, LoadAdError error) {
@@ -105,11 +110,11 @@ class _ReusableInlineExampleState extends State<ReusableInlineExample> {
         onAdLoaded: (Ad ad) {
           print('$NativeAd loaded.');
           setState(() {
-            this._nativeAdIsLoaded = true;
+            _nativeAdIsLoaded = true;
           });
         },
         onAdFailedToLoad: (Ad ad, LoadAdError error) {
-          print('$NativeAd failedToLoad: ${error}');
+          print('$NativeAd failedToLoad: $error');
           ad.dispose();
         },
         onAdOpened: (Ad ad) => print('$NativeAd onAdOpened.'),
@@ -121,12 +126,12 @@ class _ReusableInlineExampleState extends State<ReusableInlineExample> {
     _publisherBannerAd = PublisherBannerAd(
       adUnitId: '/6499/example/banner',
       request: PublisherAdRequest(nonPersonalizedAds: true),
-      sizes: [AdSize.largeBanner],
+      sizes: <AdSize>[AdSize.largeBanner],
       listener: AdListener(
         onAdLoaded: (Ad ad) {
           print('$PublisherBannerAd loaded.');
           setState(() {
-            this._publisherBannerAdIsLoaded = true;
+            _publisherBannerAdIsLoaded = true;
           });
         },
         onAdFailedToLoad: (Ad ad, LoadAdError error) {
diff --git a/packages/google_mobile_ads/example/pubspec.yaml b/packages/google_mobile_ads/example/pubspec.yaml
index 0872122c6..05294bb71 100644
--- a/packages/google_mobile_ads/example/pubspec.yaml
+++ b/packages/google_mobile_ads/example/pubspec.yaml
@@ -22,8 +22,8 @@ dependencies:
     path: ../
 
 dev_dependencies:
-  pedantic: ^1.8.0
-  e2e: ^0.2.1
+  pedantic: ^1.11.0
+  e2e: ^0.7.0
   flutter_driver:
     sdk: flutter
 
@@ -31,4 +31,4 @@ flutter:
   uses-material-design: true
 
 environment:
-  sdk: ">=2.0.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
diff --git a/packages/google_mobile_ads/ios/Classes/FLTConstants.h b/packages/google_mobile_ads/ios/Classes/FLTConstants.h
index 06d42abf0..7200d9baf 100644
--- a/packages/google_mobile_ads/ios/Classes/FLTConstants.h
+++ b/packages/google_mobile_ads/ios/Classes/FLTConstants.h
@@ -13,4 +13,4 @@
 // limitations under the License.
 
 /** Versioned request agent string. */
-#define FLT_REQUEST_AGENT_VERSIONED @"Flutter-GMA-0.11.0+4"
+#define FLT_REQUEST_AGENT_VERSIONED @"Flutter-GMA-0.12.0"
diff --git a/packages/google_mobile_ads/lib/src/ad_containers.dart b/packages/google_mobile_ads/lib/src/ad_containers.dart
index 3e2c70935..1362ec3b2 100644
--- a/packages/google_mobile_ads/lib/src/ad_containers.dart
+++ b/packages/google_mobile_ads/lib/src/ad_containers.dart
@@ -22,17 +22,13 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
-import 'package:meta/meta.dart';
 
 import 'ad_instance_manager.dart';
 
 /// Error information about why an ad load operation failed.
 class LoadAdError {
   /// Default constructor for [LoadAdError].
-  LoadAdError(this.code, this.domain, this.message)
-      : assert(code != null),
-        assert(domain != null),
-        assert(message != null);
+  LoadAdError(this.code, this.domain, this.message);
 
   /// Unique code to identify the error.
   ///
@@ -73,32 +69,33 @@ class AdRequest {
   });
 
   /// Words or phrases describing the current user activity.
-  final List<String> keywords;
+  final List<String>? keywords;
 
   /// URL string for a webpage whose content matches the app’s primary content.
   ///
   /// This webpage content is used for targeting and brand safety purposes.
-  final String contentUrl;
+  final String? contentUrl;
 
   /// Causes a device to receive test ads.
   ///
   /// The deviceId can be obtained by viewing the logcat output after creating a
   /// new ad. This method should only be used while debugging. Be sure to remove
   /// all calls to this method before releasing your app.
-  final List<String> testDevices;
+  final List<String>? testDevices;
 
   /// Non-personalized ads are ads that are not based on a user’s past behavior.
   ///
   /// For more information:
   /// https://support.google.com/admob/answer/7676680?hl=en
-  final bool nonPersonalizedAds;
+  final bool? nonPersonalizedAds;
 
   @override
-  bool operator ==(other) {
-    return this.keywords.toString() == other.keywords.toString() &&
-        this.contentUrl == other.contentUrl &&
-        this.testDevices.toString() == other.testDevices.toString() &&
-        this.nonPersonalizedAds == other.nonPersonalizedAds;
+  bool operator ==(Object other) {
+    return other is AdRequest &&
+        listEquals<String>(keywords, other.keywords) &&
+        contentUrl == other.contentUrl &&
+        listEquals<String>(testDevices, other.testDevices) &&
+        nonPersonalizedAds == other.nonPersonalizedAds;
   }
 }
 
@@ -114,30 +111,31 @@ class PublisherAdRequest {
   });
 
   /// Words or phrases describing the current user activity.
-  final List<String> keywords;
+  final List<String>? keywords;
 
   /// URL string for a webpage whose content matches the app’s primary content.
   ///
   /// This webpage content is used for targeting and brand safety purposes.
-  final String contentUrl;
+  final String? contentUrl;
 
   /// Key-value pairs used for custom targeting.
-  final Map<String, String> customTargeting;
+  final Map<String, String>? customTargeting;
 
   /// Key-value pairs used for custom targeting.
-  final Map<String, List<String>> customTargetingLists;
+  final Map<String, List<String>>? customTargetingLists;
 
   /// Non-personalized ads are ads that are not based on a user’s past behavior.
   ///
   /// For more information:
   /// https://support.google.com/admanager/answer/9005435?hl=en
-  final bool nonPersonalizedAds;
+  final bool? nonPersonalizedAds;
 
   @override
-  bool operator ==(other) {
-    return listEquals<String>(keywords, other.keywords) &&
+  bool operator ==(Object other) {
+    return other is PublisherAdRequest &&
+        listEquals<String>(keywords, other.keywords) &&
         contentUrl == other.contentUrl &&
-        mapEquals(customTargeting, other.customTargeting) &&
+        mapEquals<String, String>(customTargeting, other.customTargeting) &&
         customTargetingLists.toString() ==
             other.customTargetingLists.toString() &&
         nonPersonalizedAds == other.nonPersonalizedAds;
@@ -153,10 +151,9 @@ class PublisherAdRequest {
 class AdSize {
   /// Default constructor for [AdSize].
   const AdSize({
-    @required this.width,
-    @required this.height,
-  })  : assert(width != null),
-        assert(height != null);
+    required this.width,
+    required this.height,
+  });
 
   /// The vertical span of an ad.
   final int height;
@@ -216,8 +213,8 @@ class AdSize {
   }
 
   @override
-  bool operator ==(other) {
-    return width == other.width && height == other.height;
+  bool operator ==(Object other) {
+    return other is AdSize && width == other.width && height == other.height;
   }
 }
 
@@ -237,34 +234,34 @@ class AdListener {
   });
 
   /// Called when an ad is successfully received.
-  final void Function(Ad ad) onAdLoaded;
+  final void Function(Ad ad)? onAdLoaded;
 
   /// Called when an ad request failed.
-  final void Function(Ad ad, LoadAdError error) onAdFailedToLoad;
+  final void Function(Ad ad, LoadAdError error)? onAdFailedToLoad;
 
   /// Called when an app event is received.
-  final void Function(Ad ad, String name, String data) onAppEvent;
+  final void Function(Ad ad, String name, String data)? onAppEvent;
 
   /// Called when a click is recorded for a [NativeAd].
-  final void Function(NativeAd ad) onNativeAdClicked;
+  final void Function(NativeAd ad)? onNativeAdClicked;
 
   /// Called when an impression is recorded for a [NativeAd].
-  final void Function(NativeAd ad) onNativeAdImpression;
+  final void Function(NativeAd ad)? onNativeAdImpression;
 
   /// Called when an ad opens an overlay that covers the screen.
-  final void Function(Ad ad) onAdOpened;
+  final void Function(Ad ad)? onAdOpened;
 
   /// Called when an ad is in the process of leaving the application.
-  final void Function(Ad ad) onApplicationExit;
+  final void Function(Ad ad)? onApplicationExit;
 
   /// Called when an ad removes an overlay that covers the screen.
-  final void Function(Ad ad) onAdClosed;
+  final void Function(Ad ad)? onAdClosed;
 
   /// Called when a [RewardedAd] triggers a reward.
   final void Function(
     RewardedAd ad,
     RewardItem reward,
-  ) onRewardedAdUserEarnedReward;
+  )? onRewardedAdUserEarnedReward;
 }
 
 /// The base class for all ads.
@@ -272,9 +269,7 @@ class AdListener {
 /// A valid [adUnitId] is required.
 abstract class Ad {
   /// Default constructor, used by subclasses.
-  const Ad({@required this.adUnitId, @required this.listener})
-      : assert(adUnitId != null),
-        assert(listener != null);
+  const Ad({required this.adUnitId, required this.listener});
 
   /// Receive callbacks from [Ad] lifecycle events.
   final AdListener listener;
@@ -306,15 +301,14 @@ abstract class Ad {
 /// A valid [adUnitId] and [size] are required.
 abstract class AdWithView extends Ad {
   /// Default constructor, used by subclasses.
-  const AdWithView({@required String adUnitId, @required AdListener listener})
+  const AdWithView({required String adUnitId, required AdListener listener})
       : super(adUnitId: adUnitId, listener: listener);
 }
 
 /// An [Ad] that is overlaid on top of the UI.
 abstract class AdWithoutView extends Ad {
   /// Default constructor used by subclasses.
-  const AdWithoutView(
-      {@required String adUnitId, @required AdListener listener})
+  const AdWithoutView({required String adUnitId, required AdListener listener})
       : super(adUnitId: adUnitId, listener: listener);
 
   /// Display this on top of the application.
@@ -335,9 +329,7 @@ class AdWidget extends StatefulWidget {
   /// Default constructor for [AdWidget].
   ///
   /// [ad] must be loaded before this is added to the widget tree.
-  const AdWidget({Key key, @required this.ad})
-      : assert(ad != null),
-        super(key: key);
+  const AdWidget({Key? key, required this.ad}) : super(key: key);
 
   /// Ad to be displayed as a widget.
   final AdWithView ad;
@@ -348,22 +340,29 @@ class AdWidget extends StatefulWidget {
 
 class _AdWidgetState extends State<AdWidget> {
   bool _adIdAlreadyMounted = false;
+  bool _adLoadNotCalled = false;
 
   @override
   void initState() {
     super.initState();
-    final int adId = instanceManager.adIdFor(widget.ad);
-    if (instanceManager.isWidgetAdIdMounted(adId)) {
-      _adIdAlreadyMounted = true;
+    final int? adId = instanceManager.adIdFor(widget.ad);
+    if (adId != null) {
+      if (instanceManager.isWidgetAdIdMounted(adId)) {
+        _adIdAlreadyMounted = true;
+      }
+      instanceManager.mountWidgetAdId(adId);
+    } else {
+      _adLoadNotCalled = true;
     }
-    instanceManager.mountWidgetAdId(adId);
   }
 
   @override
   void dispose() {
     super.dispose();
-    final int adId = instanceManager.adIdFor(widget.ad);
-    instanceManager.unmountWidgetAdId(adId);
+    final int? adId = instanceManager.adIdFor(widget.ad);
+    if (adId != null) {
+      instanceManager.unmountWidgetAdId(adId);
+    }
   }
 
   @override
@@ -378,13 +377,21 @@ class _AdWidgetState extends State<AdWidget> {
             'Make sure you are not using the same ad object in more than one AdWidget.'),
       ]);
     }
+    if (_adLoadNotCalled) {
+      throw FlutterError.fromParts(<DiagnosticsNode>[
+        ErrorSummary(
+            'AdWidget requires Ad.load to be called before AdWidget is inserted into the tree'),
+        ErrorHint(
+            'Parameter ad is not loaded. Call Ad.load before AdWidget is inserted into the tree.'),
+      ]);
+    }
     if (defaultTargetPlatform == TargetPlatform.android) {
       return PlatformViewLink(
         viewType: '${instanceManager.channel.name}/ad_widget',
         surfaceFactory:
             (BuildContext context, PlatformViewController controller) {
           return AndroidViewSurface(
-            controller: controller,
+            controller: controller as AndroidViewController,
             gestureRecognizers: const <Factory<OneSequenceGestureRecognizer>>{},
             hitTestBehavior: PlatformViewHitTestBehavior.opaque,
           );
@@ -421,13 +428,11 @@ class BannerAd extends AdWithView {
   ///
   /// A valid [adUnitId], nonnull [listener], and nonnull request is required.
   BannerAd({
-    @required this.size,
-    @required String adUnitId,
-    @required AdListener listener,
-    @required this.request,
-  })  : assert(size != null),
-        assert(request != null),
-        super(adUnitId: adUnitId, listener: listener);
+    required this.size,
+    required String adUnitId,
+    required AdListener listener,
+    required this.request,
+  }) : super(adUnitId: adUnitId, listener: listener);
 
   /// Targeting information used to fetch an [Ad].
   final AdRequest request;
@@ -465,13 +470,11 @@ class PublisherBannerAd extends AdWithView {
   ///
   /// [sizes], [adUnitId], [listener], and [request] are all required values.
   PublisherBannerAd({
-    @required this.sizes,
-    @required String adUnitId,
-    @required AdListener listener,
-    @required this.request,
-  })  : assert(sizes != null),
-        assert(sizes.isNotEmpty),
-        assert(request != null),
+    required this.sizes,
+    required String adUnitId,
+    required AdListener listener,
+    required this.request,
+  })   : assert(sizes.isNotEmpty),
         super(adUnitId: adUnitId, listener: listener);
 
   /// Targeting information used to fetch an [Ad].
@@ -517,15 +520,12 @@ class NativeAd extends AdWithView {
   /// A valid [adUnitId], nonnull [listener], nonnull [request], and nonnull
   /// [factoryId] is required.
   NativeAd({
-    @required String adUnitId,
-    @required this.factoryId,
-    @required AdListener listener,
-    @required this.request,
+    required String adUnitId,
+    required this.factoryId,
+    required AdListener listener,
+    required this.request,
     this.customOptions,
   })  : publisherRequest = null,
-        assert(adUnitId != null),
-        assert(listener != null),
-        assert(factoryId != null),
         assert(request != null),
         super(adUnitId: adUnitId, listener: listener);
 
@@ -534,15 +534,12 @@ class NativeAd extends AdWithView {
   /// A valid [adUnitId], nonnull [listener], nonnull [publisherRequest], and
   /// nonnull [factoryId] is required.
   NativeAd.fromPublisherRequest({
-    @required String adUnitId,
-    @required this.factoryId,
-    @required AdListener listener,
-    @required this.publisherRequest,
+    required String adUnitId,
+    required this.factoryId,
+    required AdListener listener,
+    required this.publisherRequest,
     this.customOptions,
   })  : request = null,
-        assert(factoryId != null),
-        assert(adUnitId != null),
-        assert(listener != null),
         assert(publisherRequest != null),
         super(adUnitId: adUnitId, listener: listener);
 
@@ -552,13 +549,13 @@ class NativeAd extends AdWithView {
   /// Optional options used to create the [NativeAd].
   ///
   /// These options are passed to the platform's `NativeAdFactory`.
-  Map<String, Object> customOptions;
+  Map<String, Object>? customOptions;
 
   /// Targeting information used to fetch an [Ad].
-  final AdRequest request;
+  final AdRequest? request;
 
   /// Targeting information used to fetch an [Ad] with Ad Manager.
-  final PublisherAdRequest publisherRequest;
+  final PublisherAdRequest? publisherRequest;
 
   /// {@template google_mobile_ads.testAdUnitId}
   /// A platform-specific AdMob test ad unit ID.
@@ -584,11 +581,10 @@ class InterstitialAd extends AdWithoutView {
   /// A valid [adUnitId] from the AdMob dashboard, a nonnull [listener], and a
   /// nonnull [request] is required.
   InterstitialAd({
-    @required String adUnitId,
-    @required AdListener listener,
-    @required this.request,
-  })  : assert(request != null),
-        super(adUnitId: adUnitId, listener: listener);
+    required String adUnitId,
+    required AdListener listener,
+    required this.request,
+  }) : super(adUnitId: adUnitId, listener: listener);
 
   /// Targeting information used to fetch an [Ad].
   final AdRequest request;
@@ -611,11 +607,10 @@ class PublisherInterstitialAd extends AdWithoutView {
   /// A valid [adUnitId] from the Ad Manager dashboard, a nonnull [listener],
   /// and nonnull [request] is required.
   PublisherInterstitialAd({
-    @required String adUnitId,
-    @required AdListener listener,
-    @required this.request,
-  })  : assert(request != null),
-        super(adUnitId: adUnitId, listener: listener);
+    required String adUnitId,
+    required AdListener listener,
+    required this.request,
+  }) : super(adUnitId: adUnitId, listener: listener);
 
   /// Targeting information used to fetch an [Ad].
   final PublisherAdRequest request;
@@ -635,27 +630,27 @@ class RewardedAd extends AdWithoutView {
   ///
   /// A valid [adUnitId], nonnull [listener], and nonnull request is required.
   RewardedAd({
-    @required String adUnitId,
-    @required AdListener listener,
-    @required this.request,
-  })  : publisherRequest = null,
+    required String adUnitId,
+    required AdListener listener,
+    required this.request,
+  })   : publisherRequest = null,
         super(adUnitId: adUnitId, listener: listener);
 
   /// Creates a [RewardedAd] with a [PublisherAdRequest].
   ///
   /// A valid [adUnitId], nonnull [listener], and nonnull request is required.
   RewardedAd.fromPublisherRequest({
-    @required String adUnitId,
-    @required AdListener listener,
-    @required this.publisherRequest,
-  })  : request = null,
+    required String adUnitId,
+    required AdListener listener,
+    required this.publisherRequest,
+  })   : request = null,
         super(adUnitId: adUnitId, listener: listener);
 
   /// Targeting information used to fetch an [Ad].
-  final AdRequest request;
+  final AdRequest? request;
 
   /// Targeting information used to fetch an [Ad] using Ad Manager.
-  final PublisherAdRequest publisherRequest;
+  final PublisherAdRequest? publisherRequest;
 
   /// {@template google_mobile_ads.testAdUnitId}
   /// A platform-specific AdMob test ad unit ID.
@@ -680,9 +675,7 @@ class RewardItem {
   ///
   /// This is mostly used to return [RewardItem]s for a [RewardedAd] and
   /// shouldn't be needed to be used directly.
-  RewardItem(this.amount, this.type)
-      : assert(amount != null),
-        assert(type != null);
+  RewardItem(this.amount, this.type);
 
   /// Credit amount rewarded from a [RewardedAd].
   final num amount;
diff --git a/packages/google_mobile_ads/lib/src/ad_instance_manager.dart b/packages/google_mobile_ads/lib/src/ad_instance_manager.dart
index 055ef7fdf..5d0b62162 100644
--- a/packages/google_mobile_ads/lib/src/ad_instance_manager.dart
+++ b/packages/google_mobile_ads/lib/src/ad_instance_manager.dart
@@ -35,8 +35,7 @@ AdInstanceManager instanceManager = AdInstanceManager(
 /// Maintains access to loaded [Ad] instances.
 class AdInstanceManager {
   AdInstanceManager(String channelName)
-      : assert(channelName != null),
-        channel = MethodChannel(
+      : channel = MethodChannel(
           channelName,
           StandardMethodCodec(AdMessageCodec()),
         ) {
@@ -46,7 +45,7 @@ class AdInstanceManager {
       final int adId = call.arguments['adId'];
       final String eventName = call.arguments['eventName'];
 
-      final Ad ad = adFor(adId);
+      final Ad? ad = adFor(adId);
       if (ad != null) {
         _onAdEvent(ad, eventName, call.arguments);
       } else {
@@ -65,36 +64,36 @@ class AdInstanceManager {
   final MethodChannel channel;
 
   void _onAdEvent(Ad ad, String eventName, Map<dynamic, dynamic> arguments) {
-    assert(ad != null);
     switch (eventName) {
       case 'onAdLoaded':
         _onAdLoadedAds.add(ad);
-        ad.listener?.onAdLoaded(ad);
+        ad.listener.onAdLoaded?.call(ad);
         break;
       case 'onAdFailedToLoad':
-        ad.listener?.onAdFailedToLoad(ad, arguments['loadAdError']);
+        ad.listener.onAdFailedToLoad?.call(ad, arguments['loadAdError']);
         break;
       case 'onNativeAdClicked':
-        ad.listener?.onNativeAdClicked(ad);
+        ad.listener.onNativeAdClicked?.call(ad as NativeAd);
         break;
       case 'onNativeAdImpression':
-        ad.listener?.onNativeAdImpression(ad);
+        ad.listener.onNativeAdImpression?.call(ad as NativeAd);
         break;
       case 'onAdOpened':
-        ad.listener?.onAdOpened(ad);
+        ad.listener.onAdOpened?.call(ad);
         break;
       case 'onApplicationExit':
-        ad.listener?.onApplicationExit(ad);
+        ad.listener.onApplicationExit?.call(ad);
         break;
       case 'onAdClosed':
-        ad.listener?.onAdClosed(ad);
+        ad.listener.onAdClosed?.call(ad);
         break;
       case 'onAppEvent':
-        ad.listener?.onAppEvent(ad, arguments['name'], arguments['data']);
+        ad.listener.onAppEvent?.call(ad, arguments['name'], arguments['data']);
         break;
       case 'onRewardedAdUserEarnedReward':
         assert(arguments['rewardItem'] != null);
-        ad.listener?.onRewardedAdUserEarnedReward(ad, arguments['rewardItem']);
+        ad.listener.onRewardedAdUserEarnedReward
+            ?.call(ad as RewardedAd, arguments['rewardItem']);
         break;
       default:
         debugPrint('invalid ad event name: $eventName');
@@ -102,12 +101,12 @@ class AdInstanceManager {
   }
 
   /// Returns null if an invalid [adId] was passed in.
-  Ad adFor(int adId) => _loadedAds[adId];
+  Ad? adFor(int adId) => _loadedAds[adId];
 
   /// Returns null if an invalid [Ad] was passed in.
-  int adIdFor(Ad ad) => _loadedAds.inverse[ad];
+  int? adIdFor(Ad ad) => _loadedAds.inverse[ad];
 
-  Set<int> _mountedWidgetAdIds = <int>{};
+  final Set<int> _mountedWidgetAdIds = <int>{};
 
   /// Returns true if the [adId] is already mounted in a [WidgetAd].
   bool isWidgetAdIdMounted(int adId) => _mountedWidgetAdIds.contains(adId);
@@ -123,17 +122,16 @@ class AdInstanceManager {
   /// Loading also terminates if ad is already in the process of loading.
   Future<void> loadBannerAd(BannerAd ad) {
     if (adIdFor(ad) != null) {
-      return null;
+      return Future<void>.value();
     }
 
     final int adId = _nextAdId++;
     _loadedAds[adId] = ad;
-    final Ad bannerAd = adFor(adId);
     return channel.invokeMethod<void>(
       'loadBannerAd',
       <dynamic, dynamic>{
         'adId': adId,
-        'adUnitId': bannerAd.adUnitId,
+        'adUnitId': ad.adUnitId,
         'request': ad.request,
         'size': ad.size,
       },
@@ -142,18 +140,17 @@ class AdInstanceManager {
 
   Future<void> loadInterstitialAd(InterstitialAd ad) {
     if (adIdFor(ad) != null) {
-      return null;
+      return Future<void>.value();
     }
 
     final int adId = _nextAdId++;
     _loadedAds[adId] = ad;
-    final InterstitialAd interstitialAd = adFor(adId);
     return channel.invokeMethod<void>(
       'loadInterstitialAd',
       <dynamic, dynamic>{
         'adId': adId,
-        'adUnitId': interstitialAd.adUnitId,
-        'request': interstitialAd.request,
+        'adUnitId': ad.adUnitId,
+        'request': ad.request,
       },
     );
   }
@@ -163,17 +160,16 @@ class AdInstanceManager {
   /// Loading also terminates if ad is already in the process of loading.
   Future<void> loadNativeAd(NativeAd ad) {
     if (adIdFor(ad) != null) {
-      return null;
+      return Future<void>.value();
     }
 
     final int adId = _nextAdId++;
     _loadedAds[adId] = ad;
-    final Ad nativeAd = adFor(adId);
     return channel.invokeMethod<void>(
       'loadNativeAd',
       <dynamic, dynamic>{
         'adId': adId,
-        'adUnitId': nativeAd.adUnitId,
+        'adUnitId': ad.adUnitId,
         'request': ad.request,
         'publisherRequest': ad.publisherRequest,
         'factoryId': ad.factoryId,
@@ -187,19 +183,18 @@ class AdInstanceManager {
   /// Loading also terminates if ad is already in the process of loading.
   Future<void> loadRewardedAd(RewardedAd ad) {
     if (adIdFor(ad) != null) {
-      return null;
+      return Future<void>.value();
     }
 
     final int adId = _nextAdId++;
     _loadedAds[adId] = ad;
-    final RewardedAd rewardedAd = adFor(adId);
     return channel.invokeMethod<void>(
       'loadRewardedAd',
       <dynamic, dynamic>{
         'adId': adId,
-        'adUnitId': rewardedAd.adUnitId,
-        'request': rewardedAd.request,
-        'publisherRequest': rewardedAd.publisherRequest,
+        'adUnitId': ad.adUnitId,
+        'request': ad.request,
+        'publisherRequest': ad.publisherRequest,
       },
     );
   }
@@ -209,7 +204,7 @@ class AdInstanceManager {
   /// Loading also terminates if ad is already in the process of loading.
   Future<void> loadPublisherBannerAd(PublisherBannerAd ad) {
     if (adIdFor(ad) != null) {
-      return null;
+      return Future<void>.value();
     }
 
     final int adId = _nextAdId++;
@@ -230,7 +225,7 @@ class AdInstanceManager {
   /// Loading also terminates if ad is already in the process of loading.
   Future<void> loadPublisherInterstitialAd(PublisherInterstitialAd ad) {
     if (adIdFor(ad) != null) {
-      return null;
+      return Future<void>.value();
     }
 
     final int adId = _nextAdId++;
@@ -252,10 +247,10 @@ class AdInstanceManager {
   Future<void> disposeAd(Ad ad) {
     _onAdLoadedAds.remove(ad);
 
-    final int adId = adIdFor(ad);
-    final Ad disposedAd = _loadedAds.remove(adId);
+    final int? adId = adIdFor(ad);
+    final Ad? disposedAd = _loadedAds.remove(adId);
     if (disposedAd == null) {
-      return null;
+      return Future<void>.value();
     }
     return channel.invokeMethod<void>(
       'disposeAd',
@@ -386,7 +381,7 @@ class AdMessageCodec extends StandardMessageCodec {
           contentUrl: readValueOfType(buffer.getUint8(), buffer),
           customTargeting: readValueOfType(buffer.getUint8(), buffer)
               ?.cast<String, String>(),
-          customTargetingLists: _deepMapCast<String>(
+          customTargetingLists: _tryDeepMapCast<String>(
             readValueOfType(buffer.getUint8(), buffer),
           ),
           nonPersonalizedAds: readValueOfType(buffer.getUint8(), buffer),
@@ -404,11 +399,10 @@ class AdMessageCodec extends StandardMessageCodec {
             readValueOfType(buffer.getUint8(), buffer);
         final String description = readValueOfType(buffer.getUint8(), buffer);
 
-        double latency = readValueOfType(buffer.getUint8(), buffer)?.toDouble();
+        double latency = readValueOfType(buffer.getUint8(), buffer).toDouble();
         // Android provides this value as an int in milliseconds while iOS
         // provides this value as a double in seconds.
-        if (latency != null &&
-            defaultTargetPlatform == TargetPlatform.android) {
+        if (defaultTargetPlatform == TargetPlatform.android) {
           latency /= 1000;
         }
 
@@ -423,7 +417,7 @@ class AdMessageCodec extends StandardMessageCodec {
     }
   }
 
-  Map<String, List<T>> _deepMapCast<T>(Map<dynamic, dynamic> map) {
+  Map<String, List<T>>? _tryDeepMapCast<T>(Map<dynamic, dynamic>? map) {
     if (map == null) return null;
     return map.map<String, List<T>>(
       (dynamic key, dynamic value) => MapEntry<String, List<T>>(
@@ -442,12 +436,12 @@ class _BiMap<K extends Object, V extends Object> extends MapBase<K, V> {
   _BiMap._inverse(this._inverse);
 
   final Map<K, V> _map = <K, V>{};
-  _BiMap<V, K> _inverse;
+  late _BiMap<V, K> _inverse;
 
-  _BiMap get inverse => _inverse;
+  _BiMap<V, K> get inverse => _inverse;
 
   @override
-  V operator [](Object key) => _map[key];
+  V? operator [](Object? key) => _map[key];
 
   @override
   void operator []=(K key, V value) {
@@ -467,9 +461,9 @@ class _BiMap<K extends Object, V extends Object> extends MapBase<K, V> {
   Iterable<K> get keys => _map.keys;
 
   @override
-  V remove(Object key) {
+  V? remove(Object? key) {
     if (key == null) return null;
-    final V value = _map[key];
+    final V? value = _map[key];
     inverse._map.remove(value);
     return _map.remove(key);
   }
diff --git a/packages/google_mobile_ads/lib/src/mobile_ads.dart b/packages/google_mobile_ads/lib/src/mobile_ads.dart
index 3828f3e21..c5dfbf7c8 100644
--- a/packages/google_mobile_ads/lib/src/mobile_ads.dart
+++ b/packages/google_mobile_ads/lib/src/mobile_ads.dart
@@ -44,10 +44,10 @@ class MobileAds {
   ///
   /// If this method is not called, the first ad request automatically
   /// initializes the Google Mobile Ads SDK.
-  Future<InitializationStatus> initialize() {
-    return instanceManager.channel.invokeMethod<InitializationStatus>(
+  Future<InitializationStatus> initialize() async {
+    return (await instanceManager.channel.invokeMethod<InitializationStatus>(
       'MobileAds#initialize',
-    );
+    ))!;
   }
 
   /// Update the [RequestConfiguration] to apply for future ad requests.
@@ -59,7 +59,7 @@ class MobileAds {
   /// Internal init to cleanup state for hot restart.
   /// This is a workaround for https://github.com/flutter/flutter/issues/7160.
   void _init() {
-    instanceManager.channel.invokeMethod("_init");
+    instanceManager.channel.invokeMethod('_init');
   }
 }
 
diff --git a/packages/google_mobile_ads/lib/src/request_configuration.dart b/packages/google_mobile_ads/lib/src/request_configuration.dart
index feec75cc5..e027b5c1a 100644
--- a/packages/google_mobile_ads/lib/src/request_configuration.dart
+++ b/packages/google_mobile_ads/lib/src/request_configuration.dart
@@ -18,16 +18,16 @@
 /// https://developers.google.com/ad-manager/mobile-ads-sdk/android/targeting#requestconfiguration.
 class RequestConfiguration {
   /// Maximum content rating that will be shown.
-  final String maxAdContentRating;
+  final String? maxAdContentRating;
 
   /// Whether to tag as child directed.
-  final int tagForChildDirectedTreatment;
+  final int? tagForChildDirectedTreatment;
 
   /// Whether to tag as under age of consent.
-  final int tagForUnderAgeOfConsent;
+  final int? tagForUnderAgeOfConsent;
 
   /// List of test device ids to set.
-  final List<String> testDeviceIds;
+  final List<String>? testDeviceIds;
 
   /// Creates a [RequestConfiguration].
   RequestConfiguration(
@@ -40,19 +40,19 @@ class RequestConfiguration {
 /// Values for [RequestConfiguration.maxAdContentRating].
 class MaxAdContentRating {
   /// No specified content rating.
-  static final String unspecified = "";
+  static final String unspecified = '';
 
   /// Content suitable for general audiences, including families.
-  static final String g = "G";
+  static final String g = 'G';
 
   /// Content suitable for most audiences with parental guidance.
-  static final String pg = "PG";
+  static final String pg = 'PG';
 
   /// Content suitable for most audiences with parental guidance.
-  static final String t = "T";
+  static final String t = 'T';
 
   /// Content suitable only for mature audiences.
-  static final String ma = "MA";
+  static final String ma = 'MA';
 }
 
 /// Values for [RequestConfiguration.tagForUnderAgeOfConsent].
diff --git a/packages/google_mobile_ads/pubspec.yaml b/packages/google_mobile_ads/pubspec.yaml
index ddfe59889..27db6bf96 100644
--- a/packages/google_mobile_ads/pubspec.yaml
+++ b/packages/google_mobile_ads/pubspec.yaml
@@ -16,7 +16,7 @@ name: google_mobile_ads
 description: Flutter plugin for Google Mobile Ads, supporting
   banner, interstitial (full-screen),  rewarded and native ads
 homepage: https://github.com/googleads/googleads-mobile-flutter/tree/master/packages/google_mobile_ads
-version: 0.11.0+4
+version: 0.12.0
 
 flutter:
   plugin:
@@ -33,14 +33,14 @@ dependencies:
     sdk: flutter
 
 dev_dependencies:
-  pedantic: ^1.8.0
-  e2e: ^0.2.1
+  pedantic: ^1.11.0
+  e2e: ^0.7.0
   flutter_driver:
     sdk: flutter
-  mockito: ^3.0.0
+  mockito: ^5.0.0-0
   flutter_test:
     sdk: flutter
 
 environment:
-  sdk: ">=2.7.0 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
   flutter: ">=1.12.13+hotfix.5"
diff --git a/packages/google_mobile_ads/test/ad_containers_test.dart b/packages/google_mobile_ads/test/ad_containers_test.dart
index 8be9852e0..a9bb4961d 100644
--- a/packages/google_mobile_ads/test/ad_containers_test.dart
+++ b/packages/google_mobile_ads/test/ad_containers_test.dart
@@ -12,8 +12,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-// @dart=2.9
-
 import 'dart:async';
 
 import 'package:google_mobile_ads/src/ad_instance_manager.dart';
@@ -27,7 +25,7 @@ void main() {
 
   group('GoogleMobileAds', () {
     final List<MethodCall> log = <MethodCall>[];
-    final MessageCodec codec = AdMessageCodec();
+    final MessageCodec<dynamic> codec = AdMessageCodec();
 
     setUp(() async {
       log.clear();
@@ -58,7 +56,7 @@ void main() {
         maxAdContentRating: MaxAdContentRating.ma,
         tagForChildDirectedTreatment: TagForChildDirectedTreatment.yes,
         tagForUnderAgeOfConsent: TagForUnderAgeOfConsent.yes,
-        testDeviceIds: ["test-device-id"],
+        testDeviceIds: <String>['test-device-id'],
       );
       await instanceManager.updateRequestConfiguration(requestConfiguration);
       expect(log, <Matcher>[
@@ -67,7 +65,7 @@ void main() {
               'maxAdContentRating': MaxAdContentRating.ma,
               'tagForChildDirectedTreatment': TagForChildDirectedTreatment.yes,
               'tagForUnderAgeOfConsent': TagForUnderAgeOfConsent.yes,
-              'testDeviceIds': ['test-device-id'],
+              'testDeviceIds': <String>['test-device-id'],
             })
       ]);
     });
@@ -181,43 +179,88 @@ void main() {
     });
 
     testWidgets('build ad widget', (WidgetTester tester) async {
+      final NativeAd native = NativeAd(
+        adUnitId: NativeAd.testAdUnitId,
+        factoryId: '0',
+        listener: AdListener(),
+        request: AdRequest(),
+      );
+
+      await native.load();
+
       await tester.pumpWidget(
         Builder(
           builder: (BuildContext context) {
-            final NativeAd native = NativeAd(
-              adUnitId: NativeAd.testAdUnitId,
-              factoryId: '0',
-              listener: AdListener(),
-              request: AdRequest(),
-            );
-
             AdWidget widget = AdWidget(ad: native);
-            var buildWidget = widget.createElement().build();
+            Widget buildWidget = widget.createElement().build();
             expect(buildWidget, isA<PlatformViewLink>());
             return widget;
           },
         ),
       );
+
+      await native.dispose();
     });
 
     testWidgets('build ad widget', (WidgetTester tester) async {
+      final NativeAd native = NativeAd(
+        adUnitId: NativeAd.testAdUnitId,
+        factoryId: '0',
+        listener: AdListener(),
+        request: AdRequest(),
+      );
+
+      await native.load();
+
       await tester.pumpWidget(
         Builder(
           builder: (BuildContext context) {
-            final NativeAd native = NativeAd(
-              adUnitId: NativeAd.testAdUnitId,
-              factoryId: '0',
-              listener: AdListener(),
-              request: AdRequest(),
-            );
-
             AdWidget widget = AdWidget(ad: native);
-            var buildWidget = widget.createElement().build();
+            Widget buildWidget = widget.createElement().build();
             expect(buildWidget, isA<PlatformViewLink>());
             return widget;
           },
         ),
       );
+
+      await native.dispose();
+    });
+
+    testWidgets('warns when ad has not been loaded',
+        (WidgetTester tester) async {
+      final NativeAd ad = NativeAd(
+        adUnitId: NativeAd.testAdUnitId,
+        factoryId: '0',
+        listener: AdListener(),
+        request: AdRequest(),
+      );
+
+      try {
+        await tester.pumpWidget(
+          Directionality(
+            textDirection: TextDirection.ltr,
+            child: SizedBox(
+              width: 100,
+              height: 100,
+              child: Stack(
+                children: <Widget>[
+                  AdWidget(ad: ad),
+                ],
+              ),
+            ),
+          ),
+        );
+      } finally {
+        dynamic exception = tester.takeException();
+        expect(exception, isA<FlutterError>());
+        expect(
+            (exception as FlutterError).toStringDeep(),
+            'FlutterError\n'
+            '   AdWidget requires Ad.load to be called before AdWidget is\n'
+            '   inserted into the tree\n'
+            '   Parameter ad is not loaded. Call Ad.load before AdWidget is\n'
+            '   inserted into the tree.\n');
+      }
     });
 
     testWidgets('warns when ad object is reused', (WidgetTester tester) async {
@@ -451,7 +494,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(adEventCompleter.future, completion(banner));
@@ -484,7 +527,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       final List<dynamic> results = await resultsCompleter.future;
@@ -516,7 +559,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(adEventCompleter.future, completion(native));
@@ -544,7 +587,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(adEventCompleter.future, completion(native));
@@ -572,7 +615,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(adEventCompleter.future, completion(banner));
@@ -600,7 +643,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(adEventCompleter.future, completion(banner));
@@ -628,7 +671,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(adEventCompleter.future, completion(banner));
@@ -661,7 +704,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       final List<dynamic> result = await resultCompleter.future;
@@ -698,25 +741,25 @@ void main() {
     });
 
     test('encode/decode AdSize', () async {
-      final ByteData byteData = codec.encodeMessage(AdSize.banner);
+      final ByteData byteData = codec.encodeMessage(AdSize.banner)!;
       expect(codec.decodeMessage(byteData), AdSize.banner);
     });
 
     test('encode/decode AdRequest', () async {
       final AdRequest adRequest = AdRequest(
-          keywords: ['1', '2', '3'],
+          keywords: <String>['1', '2', '3'],
           contentUrl: 'contentUrl',
-          testDevices: ['Android', 'iOS'],
+          testDevices: <String>['Android', 'iOS'],
           nonPersonalizedAds: false);
 
-      final ByteData byteData = codec.encodeMessage(adRequest);
+      final ByteData byteData = codec.encodeMessage(adRequest)!;
       expect(codec.decodeMessage(byteData), adRequest);
     });
 
     test('encode/decode $LoadAdError', () async {
       final ByteData byteData = codec.encodeMessage(
         LoadAdError(1, 'domain', 'message'),
-      );
+      )!;
       final LoadAdError error = codec.decodeMessage(byteData);
       expect(error.code, 1);
       expect(error.domain, 'domain');
@@ -724,7 +767,7 @@ void main() {
     });
 
     test('encode/decode $RewardItem', () async {
-      final ByteData byteData = codec.encodeMessage(RewardItem(1, 'type'));
+      final ByteData byteData = codec.encodeMessage(RewardItem(1, 'type'))!;
 
       final RewardItem result = codec.decodeMessage(byteData);
       expect(result.amount, 1);
@@ -740,7 +783,7 @@ void main() {
           'him': <String>['is']
         },
         nonPersonalizedAds: true,
-      ));
+      ))!;
 
       expect(
         codec.decodeMessage(byteData),
@@ -783,7 +826,7 @@ void main() {
       await instanceManager.channel.binaryMessenger.handlePlatformMessage(
         'plugins.flutter.io/google_mobile_ads',
         data,
-        (ByteData data) {},
+        (ByteData? data) {},
       );
 
       expect(banner.isLoaded(), completion(true));
diff --git a/packages/google_mobile_ads/test/mobile_ads_test.dart b/packages/google_mobile_ads/test/mobile_ads_test.dart
index 3afb15b96..ca7636e5f 100644
--- a/packages/google_mobile_ads/test/mobile_ads_test.dart
+++ b/packages/google_mobile_ads/test/mobile_ads_test.dart
@@ -42,7 +42,7 @@ void main() {
               'aName': AdapterStatus(
                 AdapterInitializationState.notReady,
                 'desc',
-                null,
+                0,
               ),
             });
           case '_init':
@@ -56,7 +56,7 @@ void main() {
 
     test('encode/decode $AdapterInitializationState', () {
       final ByteData byteData =
-          codec.encodeMessage(AdapterInitializationState.ready);
+          codec.encodeMessage(AdapterInitializationState.ready)!;
 
       final AdapterInitializationState result = codec.decodeMessage(byteData);
       expect(result, AdapterInitializationState.ready);
@@ -68,7 +68,7 @@ void main() {
         AdapterInitializationState.notReady,
         'describe',
         23,
-      ));
+      ))!;
 
       AdapterStatus result = codec.decodeMessage(byteData);
       expect(result.state, AdapterInitializationState.notReady);
@@ -85,7 +85,7 @@ void main() {
     test('handle int values for AdapterStatus', () {
       final WriteBuffer buffer = WriteBuffer();
       codec.writeValue(buffer, AdapterInitializationState.ready);
-      codec.writeValue(buffer, null);
+      codec.writeValue(buffer, 'aDescription');
       codec.writeValue(buffer, 23);
 
       expect(
@@ -103,31 +103,31 @@ void main() {
         'adMediation': AdapterStatus(
           AdapterInitializationState.ready,
           'aDescription',
-          null,
+          0,
         ),
-      }));
+      }))!;
 
       final InitializationStatus result = codec.decodeMessage(byteData);
       expect(result.adapterStatuses, hasLength(1));
-      final AdapterStatus status = result.adapterStatuses['adMediation'];
+      final AdapterStatus status = result.adapterStatuses['adMediation']!;
       expect(status.state, AdapterInitializationState.ready);
       expect(status.description, 'aDescription');
-      expect(status.latency, null);
+      expect(status.latency, 0);
     });
 
     test('$MobileAds.initialize', () async {
       final InitializationStatus result = await MobileAds.instance.initialize();
 
       expect(log, <Matcher>[
-        isMethodCall("_init", arguments: null),
-        isMethodCall("MobileAds#initialize", arguments: null)
+        isMethodCall('_init', arguments: null),
+        isMethodCall('MobileAds#initialize', arguments: null)
       ]);
 
       expect(result.adapterStatuses, hasLength(1));
-      final AdapterStatus status = result.adapterStatuses['aName'];
+      final AdapterStatus status = result.adapterStatuses['aName']!;
       expect(status.state, AdapterInitializationState.notReady);
       expect(status.description, 'desc');
-      expect(status.latency, null);
+      expect(status.latency, 0);
     });
   });
 }