code: public KVStore toKVStore() {
          KVStore store = new KVStore();
          store.putValue("status", statusCode());
          store.putValue("message", getLocalizedMessage());
          store.putValue("timestamp", timestamp());
          Integer code = errorCode();
          if (null != code) {
              store.putValue("code", code);
          }
          Object payload = attachment();
          if (null != payload) {
              store.putValue("payload", payload);
          }
          return store;
      }
docs: Export the error result data into a {@link KVStore}
  @return a {@link KVStore KV store} of this error result