code: void checkPinBoxesAvailableOrder() {
  
          int index = -1;
          for (int i = 0; i < mNumberPinBoxes; i++) {
              if (pinBoxIsEmpty(i)) {
                  index = i;
                  break;
              }
          }
          chooseNextAction(index);
      }
docs: Check for an empty PinBox {@link EditText} from the first.
  Set focus in the first empty PinBox or notify that {@link PinView} is completed.