[webview_flutter_wkwebview] Fixes an exception caused by the onUrlChange callback returning a null url (#3848)

While investigating another bug, I realized that loading the initial request with an invalid url, the callback returns a null NSURL.

Author: bparrishMines

packages/webview_flutter/webview_flutter_wkwebview/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.4.2
+
+* Fixes an exception caused by the `onUrlChange` callback passing a null `NSUrl`.
+
 ## 3.4.1
 
 * Fixes internal type conversion error.

packages/webview_flutter/webview_flutter_wkwebview/lib/src/webkit_webview_controller.dart

@@ -239,8 +239,8 @@ class WebKitWebViewController extends PlatformWebViewController {
             final UrlChangeCallback? urlChangeCallback =
                 controller._currentNavigationDelegate?._onUrlChange;
             if (urlChangeCallback != null) {
-              final NSUrl url = change[NSKeyValueChangeKey.newValue]! as NSUrl;
-              urlChangeCallback(UrlChange(url: await url.getAbsoluteString()));
+              final NSUrl? url = change[NSKeyValueChangeKey.newValue] as NSUrl?;
+              urlChangeCallback(UrlChange(url: await url?.getAbsoluteString()));
             }
             break;
         }

packages/webview_flutter/webview_flutter_wkwebview/pubspec.yaml

@@ -2,7 +2,7 @@ name: webview_flutter_wkwebview
 description: A Flutter plugin that provides a WebView widget based on Apple's WKWebView control.
 repository: https://github.com/flutter/packages/tree/main/packages/webview_flutter/webview_flutter_wkwebview
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 3.4.1
+version: 3.4.2
 
 environment:
   sdk: ">=2.18.0 <4.0.0"

packages/webview_flutter/webview_flutter_wkwebview/test/webkit_webview_controller_test.dart

@@ -1036,6 +1036,56 @@ void main() {
       expect(urlChange.url, 'https://www.google.com');
     });
 
+    test('setPlatformNavigationDelegate onUrlChange to null NSUrl', () async {
+      final MockWKWebView mockWebView = MockWKWebView();
+
+      late final void Function(
+        String keyPath,
+        NSObject object,
+        Map<NSKeyValueChangeKey, Object?> change,
+      ) webViewObserveValue;
+
+      final WebKitWebViewController controller = createControllerWithMocks(
+        createMockWebView: (
+          _, {
+          void Function(
+            String keyPath,
+            NSObject object,
+            Map<NSKeyValueChangeKey, Object?> change,
+          )? observeValue,
+        }) {
+          webViewObserveValue = observeValue!;
+          return mockWebView;
+        },
+      );
+
+      final WebKitNavigationDelegate navigationDelegate =
+          WebKitNavigationDelegate(
+        const WebKitNavigationDelegateCreationParams(
+          webKitProxy: WebKitProxy(
+            createNavigationDelegate: CapturingNavigationDelegate.new,
+            createUIDelegate: WKUIDelegate.detached,
+          ),
+        ),
+      );
+
+      final Completer<UrlChange> urlChangeCompleter = Completer<UrlChange>();
+      navigationDelegate.setOnUrlChange(
+        (UrlChange change) => urlChangeCompleter.complete(change),
+      );
+
+      await controller.setPlatformNavigationDelegate(navigationDelegate);
+
+      webViewObserveValue(
+        'URL',
+        mockWebView,
+        <NSKeyValueChangeKey, Object?>{NSKeyValueChangeKey.newValue: null},
+      );
+
+      final UrlChange urlChange = await urlChangeCompleter.future;
+      expect(urlChange.url, isNull);
+    });
+
     test('webViewIdentifier', () {
       final InstanceManager instanceManager = InstanceManager(
         onWeakReferenceRemoved: (_) {},