anchor.diff:      notifyListeners();
     }
   
  +  /// iterates through passed in topics list
  +  /// invokes [unsubscribeFromTopic] on firebase object [_fcm]
     void _subscribeToTopics(List<String> topics) {
       for (String topic in topics) {
         if ((topic ?? "").isNotEmpty) {
  
positive.code:         }
        }
        _topicSubscriptionState = newTopics;
      }
    }
  
    Map<String, dynamic> _readAndroidBuildData(AndroidDeviceInfo build) {
      return <String, dynamic>{
        'version.securityPatch': build.version.securityPatch,
  
negative.code:   /// get all public topics
    List<String> publicTopics() {
      List<String> topicsToReturn = List<String>();
      for (TopicsModel model in _topicsModel) {
        if (model.audienceId == 'all') {
          for (Topic topic in model.topics) {
            topicsToReturn.add(topic.topicId);
  