code: @Override
      public Observable<ComapiResult<String>> createFbOptInState() {
  
          final String token = getToken();
  
          if (sessionController.isCreatingSession()) {
              return getTaskQueue().createFbOptInState();
          } else if (TextUtils.isEmpty(token)) {
              return Observable.error(getSessionStateErrorDescription());
          } else {
              return doCreateFbOptInState(token);
          }
      }
docs: Gets the Facebook data-ref to create send to messenger button.
  
  @return @return Observable to get Facebook data-ref.