[plugin_platform_interface] Use Mockito nnbd (flutter#3437)

Author: Emmanuel Garcia

packages/plugin_platform_interface/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 1.1.0-nullsafety.2
+
+* Use Mockito null safe.
+
 ## 1.1.0-nullsafety.1
 
 * Bump Dart SDK to support null safety.

packages/plugin_platform_interface/lib/plugin_platform_interface.dart

@@ -43,7 +43,7 @@ abstract class PlatformInterface {
   /// Pass a private, class-specific `const Object()` as the `token`.
   PlatformInterface({required Object token}) : _instanceToken = token;
 
-  final Object _instanceToken;
+  final Object? _instanceToken;
 
   /// Ensures that the platform instance has a token that matches the
   /// provided token and throws [AssertionError] if not.

packages/plugin_platform_interface/pubspec.yaml

@@ -12,7 +12,7 @@ description: Reusable base class for Flutter plugin platform interfaces.
 # be done when absolutely necessary and after the ecosystem has already migrated to 1.X.Y version
 # that is forward compatible with 2.0.0 (ideally the ecosystem have migrated to depend on:
 # `plugin_platform_interface: >=1.X.Y <3.0.0`).
-version: 1.1.0-nullsafety.1
+version: 1.1.0-nullsafety.2
 
 repository: https://github.com/flutter/plugins/tree/master/packages/plugin_platform_interface
 
@@ -23,6 +23,6 @@ dependencies:
   meta: ^1.3.0-nullsafety.3
 
 dev_dependencies:
-  mockito: ^4.1.1
+  mockito: ^5.0.0-nullsafety.2
   test: ^1.10.0-nullsafety.1
   pedantic: ^1.10.0-nullsafety.1

packages/plugin_platform_interface/test/plugin_platform_interface_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.
 
-// TODO(egarciad): Remove once Mockito is migrated to null safety.
-// @dart = 2.9
 import 'package:mockito/mockito.dart';
 import 'package:test/test.dart';