docs: @Override
      public void validate() {
          boolean valid = true;
          if (hasValue()) {
              Long value = getValue();
              if (value != null) {
                  // scrub the value to format properly
                  setText(value2text(value));
              }
              else {
                  // empty is ok and value != null ok, this is invalid
                  valid = false;
              }
          }
          setStyleName(CLASSNAME_INVALID, !valid);
      }