code: protected synchronized boolean reject(JoynrException error) {
          if (isSettled()) {
              return false;
          }
          state = State.REJECTED;
          this.error = error;
          notifyListeners();
          return true;
      }
docs: Rejects the promise. NOTE: The thread rejecting the promise will be used
  to execute waiting listeners.
  @param error the reason that caused the rejection.
  @return true if the promise is rejected; false in case the promise is
  already settled.