anchor.diff:    /// it.
     static const _notificationDuration = Duration(days: 1);
   
  -  DevToolsSurvey _cachedSurvey;
  +  DevToolsSurvey? _cachedSurvey;
   
  -  Future<DevToolsSurvey> get activeSurvey async {
  +  Future<DevToolsSurvey?> get activeSurvey async {
       // If the server is unavailable we don't need to do anything survey related.
       if (!server.isDevToolsServerAvailable) return null;
   
       _cachedSurvey ??= await _fetchSurveyContent();
       if (_cachedSurvey != null) {
  -      await server.setActiveSurvey(_cachedSurvey.id);
  +      await server.setActiveSurvey(_cachedSurvey!.id);
       }
   
       if (await _shouldShowSurvey()) {
  
positive.code:     return DevToolsSurvey._(id, startDate, endDate, title, surveyUrl);
    }
  
    final String id;
  
    final DateTime startDate;
  
    final DateTime endDate;
  
    final String title;
  
    final String url;
  }
  
negative.code:         NotificationAction(
            _takeSurveyLabel,
            () => _takeSurveyPressed(
              surveyUrl: _generateSurveyUrl(survey.url!),
              message: message,
              context: context,
            ),
            isPrimary: true,
          ),
        ];
        WidgetsBinding.instance!.addPostFrameCallback((_) {
          final didPush = Notifications.of(context)!.push(
            message,
            actions: actions,
            duration: _notificationDuration,
  