docs: @NonNull
      public IntentServiceTokenController attachIntentServiceTokenController(
              @NonNull Activity activity,
              @NonNull Button button) {
          if (mIntentServiceTokenController == null) {
              mIntentServiceTokenController = new IntentServiceTokenController(
                      activity,
                      button,
                      mCardInputWidget,
                      mErrorDialogHandler,
                      mListViewController,
                      mProgressDialogController);
          }
          return mIntentServiceTokenController;
      }