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