NoSuchMethodError在null上调用了方法getNotification

Question

我在调用方法时得到null。我什至尝试调试，但坚持使用expect(isOPDSAgent(ua)).to.be.ok;，但不知道为什么我会得到null。调试后，我完全迷失了所缺少的东西，下面是该设备的代码和屏幕截图。也许有人可以帮助我解决零点异常

主页

getNotification()

Notification_bloc

child: BlocListener<NotificationBloc, NotificationState>(
                listener: (context, state) {
                },
                child: BlocBuilder<NotificationBloc, NotificationState>(
                  builder: (context, state) {
                    if(state is InitialNotificationState) {
                      return buildLoading();
                    }
                    else if (state is NotificationLoadedState) {
                      return NotificationIconBuild(state.notification);
                    }
                    else if(state is NotificationErrorState) {
                      return buildErrorUi(state.message1);
                    }
                  },

NotificationRepository

class NotificationBloc extends Bloc<NotificationEvent, NotificationState> {
  NotificationsRepositoryImp notificationsRepository;
  NotificationBloc({@required this.notificationsRepository});
  @override
  NotificationState get initialState => InitialNotificationState();
  @override
  Stream<NotificationState> mapEventToState(
    NotificationEvent event,
  ) async* {
    if(event is FetchNotificationEvent){
      try {
        NotificationModle notification = await notificationsRepository.getNotifications();
        yield NotificationLoadedState(notification: notification);
      }
      catch (e) {
        yield NotificationErrorState(message1: e.toString());
      }
    }

是blocbuilder中的问题吗，因为在主页中我添加了两个blocbuilder。