code: public boolean isSet(_Fields field) {
      if (field == null) {
        throw new IllegalArgumentException();
      }
  
      switch (field) {
      case NAME_TYPES:
        return isSetName_types();
      case VALUE_TYPES:
        return isSetValue_types();
      case DEFAULT_NAME_TYPE:
        return isSetDefault_name_type();
      case DEFAULT_VALUE_TYPE:
        return isSetDefault_value_type();
      }
      throw new IllegalStateException();
    }
docs: Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise