anchor.diff:  
     @override
     FutureOr<void> processOfflineData(String offlineData) async {
  -    await controller.processOfflineData(offlineData);
  +    await controller!.processOfflineData(offlineData);
     }
   
     @override
  
positive.code: 
    @override
    Widget build(BuildContext context) {
      final exampleScreen = ValueListenableBuilder(
        valueListenable: controller.title,
        builder: (context, value, _) {
          return Center(child: Text(value));
        },
      );
  
negative.code: // Copyright 2020 The Chromium Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  import 'dart:async';
  
  