code: private void checkApplyParams(RefundApplyRequest request) {
          checkNotNull(wepay.certs, "merchant certs can't be null before apply refund");
          checkNotNullAndEmpty(wepay.certPasswd, "certPasswd");
          checkNotNull(request, "apply request can't be null");
          if (Strings.isNullOrEmpty(request.getTransactionId())){
              checkNotNullAndEmpty(request.getOutTradeNo(), "transactionId && outTradeNo");
          }
          checkNotNullAndEmpty(request.getOutRefundNo(), "outRefundNo");
          checkNotNullAndEmpty(request.getOpUserId(), "opUserId");
          Integer totalFee = request.getTotalFee();
          Integer refundFee = request.getRefundFee();
          checkPositive(totalFee, "totalFee");
          checkPositive(refundFee, "refundFee");
          checkPositive(totalFee - refundFee, "totalFee - refundFee");
      }
docs: 校验退款参数
  @param request 退款请求对象