anchor.diff:  class _ExampleConditionalScreenBodyState
       extends State<_ExampleConditionalScreenBody>
       with OfflineScreenMixin<_ExampleConditionalScreenBody, String> {
  -  ExampleController controller;
  +  ExampleController? controller;
   
     @override
     void didChangeDependencies() {
  
positive.code: 
    @override
    Widget build(BuildContext context) {
      final exampleScreen = ValueListenableBuilder(
        valueListenable: controller.title,
        builder: (context, value, _) {
          return Center(child: Text(value));
        },
      );
  
negative.code: 
    @override
    FutureOr<void> processOfflineData(String offlineData) async {
      await controller!.processOfflineData(offlineData);
    }
  
    @override
  