Fixed _CastError when running example App (#4390)

diff --git a/packages/webview_flutter/webview_flutter/CHANGELOG.md b/packages/webview_flutter/webview_flutter/CHANGELOG.md
index 92ac557..6724b43 100644
--- a/packages/webview_flutter/webview_flutter/CHANGELOG.md
+++ b/packages/webview_flutter/webview_flutter/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.1.1
+
+* Fixed `_CastError` that was thrown when running the example App.
+
 ## 2.1.0
 
 * Migrated to fully federated architecture.
diff --git a/packages/webview_flutter/webview_flutter/example/lib/main.dart b/packages/webview_flutter/webview_flutter/example/lib/main.dart
index 88256cc..c456a96 100644
--- a/packages/webview_flutter/webview_flutter/example/lib/main.dart
+++ b/packages/webview_flutter/webview_flutter/example/lib/main.dart
@@ -302,7 +302,7 @@
           (BuildContext context, AsyncSnapshot<WebViewController> snapshot) {
         final bool webViewReady =
             snapshot.connectionState == ConnectionState.done;
-        final WebViewController controller = snapshot.data!;
+        final WebViewController? controller = snapshot.data;
         return Row(
           children: <Widget>[
             IconButton(
@@ -310,7 +310,7 @@
               onPressed: !webViewReady
                   ? null
                   : () async {
-                      if (await controller.canGoBack()) {
+                      if (await controller!.canGoBack()) {
                         await controller.goBack();
                       } else {
                         // ignore: deprecated_member_use
@@ -326,7 +326,7 @@
               onPressed: !webViewReady
                   ? null
                   : () async {
-                      if (await controller.canGoForward()) {
+                      if (await controller!.canGoForward()) {
                         await controller.goForward();
                       } else {
                         // ignore: deprecated_member_use
@@ -343,7 +343,7 @@
               onPressed: !webViewReady
                   ? null
                   : () {
-                      controller.reload();
+                      controller!.reload();
                     },
             ),
           ],
diff --git a/packages/webview_flutter/webview_flutter/pubspec.yaml b/packages/webview_flutter/webview_flutter/pubspec.yaml
index ab87063..4206789 100644
--- a/packages/webview_flutter/webview_flutter/pubspec.yaml
+++ b/packages/webview_flutter/webview_flutter/pubspec.yaml
@@ -2,7 +2,7 @@
 description: A Flutter plugin that provides a WebView widget on Android and iOS.
 repository: https://github.com/flutter/plugins/tree/master/packages/webview_flutter/webview_flutter
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 2.1.0
+version: 2.1.1
 
 environment:
   sdk: ">=2.14.0 <3.0.0"