code: public boolean isSet(_Fields field) {
      if (field == null) {
        throw new IllegalArgumentException();
      }
  
      switch (field) {
      case NAME:
        return isSetName();
      case VALIDATION_CLASS:
        return isSetValidation_class();
      case INDEX_TYPE:
        return isSetIndex_type();
      case INDEX_NAME:
        return isSetIndex_name();
      case INDEX_OPTIONS:
        return isSetIndex_options();
      }
      throw new IllegalStateException();
    }
docs: Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise