code: public RefundQueryResponse queryByTransactionId(String transactionId){
          Map<String, String> queryParams = buildQueryParams(WepayField.TRANSACTION_ID, transactionId);
          Map<String, Object> respData = doPost(QUERY, queryParams);
          return renderQueryResp(respData);
      }
docs: 通过微信订单号查询退款
  @param transactionId 微信订单号
  @return 退款查询对象，或抛WepayException