C#访问SOAP Web Service时500报错后的返回信息获取

            //500 error but get the message
            HttpWebResponse res;
            try
            {
                res = (HttpWebResponse)webRequest.GetResponse();
            }
            catch (WebException ex)
            {
                res = (HttpWebResponse)ex.Response;
            }
            StreamReader sr = new StreamReader(res.GetResponseStream() ?? throw new InvalidOperationException(), Encoding.UTF8);
            var result = sr.ReadToEnd();