使用HttpWebRequest采集一个网站的信息，需要设置Referer,直接使用request.Headers.Add(name,value)的方法报错：

System.ArgumentException:“必须使用适当的属性或方法修改“Referer”标头。
Parameter name: name”

public static string FetchHtml(string url, Encoding en)
        {
            if (en == null) en = Encoding.UTF8;
            String html;
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
            request.Timeout = 600000 ;
            
            
            request.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:82.0) Gecko/20100101 Firefox/82.0";
         
            request.Headers.Add("Referer", "https://www.baidu.com");
          
            WebResponse response = request.GetResponse();

            Stream dataStream = response.GetResponseStream();
            StreamReader reader = new StreamReader(dataStream, en);
            String responseFromServer = reader.ReadToEnd();
            html = responseFromServer;
            Encoding en2 = GetEncoding(response.ContentType);//responseFromServer
            reader.Close();
            response.Close();
            //if (en2.EncodingName != en.EncodingName)
            //{
            //    Stream htmlStream = WebRequest.Create(url).GetResponse().GetResponseStream();
            //    StreamReader htmlReader = new StreamReader(htmlStream, en2);
            //    html = htmlReader.ReadToEnd();
            //}
            //彻底过滤 \r \n
            Regex regex = new Regex(@"\r\n", RegexOptions.IgnoreCase);
            html = regex.Replace(html, "");
            regex = new Regex(@"\t", RegexOptions.IgnoreCase);
            html = regex.Replace(html, "");
    &nbs