docs: @NonNull
      public RxTokenController attachRxTokenController(Button button) {
          if (mRxTokenController == null) {
              mRxTokenController = new RxTokenController(
                      button,
                      mCardInputWidget,
                      mContext,
                      mErrorDialogHandler,
                      mListViewController,
                      mProgressDialogController);
          }
          return mRxTokenController;
      }