code: Observable<RxComapiClient> checkState() {
  
          final RxComapiClient client = clientReference.get();
          if (client == null) {
              return Observable.error(new ComapiException("No client instance available in controller."));
          } else {
              return Observable.fromCallable(() -> client);
          }
      }
docs: Checks if controller state is correct.
  
  @return Foundation client instance.