code: public boolean isSet(_Fields field) {
      if (field == null) {
        throw new IllegalArgumentException();
      }
  
      switch (field) {
      case KEY:
        return isSetKey();
      case VALUE:
        return isSetValue();
      case VALUE_CLASS:
        return isSetValueClass();
      case CREATION_TIMESTAMP_MS:
        return isSetCreationTimestampMs();
      case LAST_ACCESS_TIMESTAMP_MS:
        return isSetLastAccessTimestampMs();
      case EXPIRE_AFTER_WRITE:
        return isSetExpireAfterWrite();
      case EXPIRE_AFTER_ACCESS:
        return isSetExpireAfterAccess();
      }
      throw new IllegalStateException();
    }
docs: Returns true if field corresponding to fieldID is set (has been assigned a value) and false otherwise