[url_launcher] Migrates Link to null safety

packages/url_launcher/url_launcher/lib/src/link.dart

@@ -40,7 +40,7 @@ class Link extends StatelessWidget implements LinkInfo {
   final LinkWidgetBuilder builder;
 
   /// The destination that this link leads to.
-  final Uri uri;
+  final Uri? uri;
 
   /// The target indicating where to open the link.
   final LinkTarget target;
@@ -51,12 +51,11 @@ class Link extends StatelessWidget implements LinkInfo {
   /// Creates a widget that renders a real link on the web, and uses WebViews in
   /// native platforms to open links.
   Link({
-    Key key,
-    @required this.uri,
-    LinkTarget target,
-    @required this.builder,
-  })  : target = target ?? LinkTarget.defaultTarget,
-        super(key: key);
+    Key? key,
+    required this.uri,
+    this.target = LinkTarget.defaultTarget,
+    required this.builder,
+  }) : super(key: key);
 
   LinkDelegate get _effectiveDelegate {
     return UrlLauncherPlatform.instance.linkDelegate ??
@@ -90,16 +89,17 @@ class DefaultLinkDelegate extends StatelessWidget {
   bool get _useWebView {
     if (link.target == LinkTarget.self) return true;
     if (link.target == LinkTarget.blank) return false;
-    return null;
+    return false;
   }
 
   Future<void> _followLink(BuildContext context) async {
-    if (!link.uri.hasScheme) {
+    if (!link.uri!.hasScheme) {
       // A uri that doesn't have a scheme is an internal route name. In this
       // case, we push it via Flutter's navigation system instead of letting the
       // browser handle it.
       final String routeName = link.uri.toString();
-      return pushRouteNameToFramework(context, routeName);
+      await pushRouteNameToFramework(context, routeName);
+      return;
     }
 
     // At this point, we know that the link is external. So we use the `launch`
@@ -119,7 +119,6 @@ class DefaultLinkDelegate extends StatelessWidget {
         context: ErrorDescription('during launching a link'),
       ));
     }
-    return Future<void>.value(null);
   }
 
   @override

packages/url_launcher/url_launcher/test/link_test.dart

@@ -2,7 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
+// TODO(egarciad): Remove once Mockito has been migrated to null safety.
+// @dart = 2.9
 
 import 'dart:ui';
 import 'package:flutter/material.dart';

packages/url_launcher/url_launcher_platform_interface/lib/link.dart

@@ -16,7 +16,7 @@ typedef FollowLink = Future<void> Function();
 /// the widget tree under it.
 typedef LinkWidgetBuilder = Widget Function(
   BuildContext context,
-  FollowLink followLink,
+  FollowLink? followLink,
 );
 
 /// Signature for a delegate function to build the [Link] widget.
@@ -31,7 +31,7 @@ final MethodCodec _codec = const JSONMethodCodec();
 class LinkTarget {
   /// Const private constructor with a [debugLabel] to allow the creation of
   /// multiple distinct const instances.
-  const LinkTarget._({this.debugLabel});
+  const LinkTarget._({required this.debugLabel});
 
   /// Used to distinguish multiple const instances of [LinkTarget].
   final String debugLabel;
@@ -64,7 +64,7 @@ abstract class LinkInfo {
   LinkWidgetBuilder get builder;
 
   /// The destination that this link leads to.
-  Uri get uri;
+  Uri? get uri;
 
   /// The target indicating where to open the link.
   LinkTarget get target;
@@ -80,10 +80,14 @@ Future<ByteData> pushRouteNameToFramework(
   String routeName, {
   @visibleForTesting bool debugForceRouter = false,
 }) {
+  final PlatformMessageCallback? onPlatformMessage = window.onPlatformMessage;
+  if (onPlatformMessage == null) {
+    return Future<ByteData>.value(null);
+  }
   final Completer<ByteData> completer = Completer<ByteData>();
   if (debugForceRouter || _hasRouter(context)) {
     SystemNavigator.routeInformationUpdated(location: routeName);
-    window.onPlatformMessage(
+    onPlatformMessage(
       'flutter/navigation',
       _codec.encodeMethodCall(
         MethodCall('pushRouteInformation', <dynamic, dynamic>{
@@ -94,7 +98,7 @@ Future<ByteData> pushRouteNameToFramework(
       completer.complete,
     );
   } else {
-    window.onPlatformMessage(
+    onPlatformMessage(
       'flutter/navigation',
       _codec.encodeMethodCall(MethodCall('pushRoute', routeName)),
       completer.complete,

packages/url_launcher/url_launcher_platform_interface/lib/method_channel_url_launcher.dart

@@ -14,7 +14,7 @@ const MethodChannel _channel = MethodChannel('plugins.flutter.io/url_launcher');
 /// An implementation of [UrlLauncherPlatform] that uses method channels.
 class MethodChannelUrlLauncher extends UrlLauncherPlatform {
   @override
-  final LinkDelegate linkDelegate = null;
+  final LinkDelegate? linkDelegate = null;
 
   @override
   Future<bool> canLaunch(String url) {

packages/url_launcher/url_launcher_platform_interface/lib/url_launcher_platform_interface.dart

@@ -39,7 +39,7 @@ abstract class UrlLauncherPlatform extends PlatformInterface {
   }
 
   /// The delegate used by the Link widget to build itself.
-  LinkDelegate get linkDelegate;
+  LinkDelegate? get linkDelegate;
 
   /// Returns `true` if this platform is able to launch [url].
   Future<bool> canLaunch(String url) {

packages/url_launcher/url_launcher_platform_interface/test/link_test.dart

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// TODO(egarciad): Remove once Mockito has been migrated to null safety.
+// @dart = 2.9
+
 import 'dart:ui';
 
 import 'package:mockito/mockito.dart';