我理解的人脸注册的意思是，跟百度页面人脸库添加一样，输入一个id，添加一张图片，用户组里面，不知道有没有错误，现在执行以下代码，一直提示user_id为空  ，这个user_id不论我输入已有的还是输入一个新的，都提示user_id参数is null    addFace("http://p1.so.qhimgs1.com/bdr/592__/t01a9f7f11254e3cffd.jpg", "URL", "LT", "yonghuid", "yonghuxinxi")

    public static string addFace(string image, string imageType, string groupId, string userId, string userInfo)
        {
            string token = AccessToken.getAccessToken();
            string host = "https://aip.baidubce.com/rest/2.0/face/v3/faceset/user/add?access_token=" + token;
            Encoding encoding = Encoding.Default;
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(host);
            request.Method = "post";
            request.KeepAlive = true;
            String str = "{\"image\":\"" + image + "\",\"image_type\":\"" + imageType + "\",\"group_id\":\"" + groupId + "\",\"user_id\":\""+userId+ "\",\"user_info\":\"" + userInfo + "\",\"quality_control\":\"LOW\",\"liveness_control\":\"NORMAL\"}";
            byte[] buffer = encoding.GetBytes(str);
            request.ContentLength = buffer.Length;
            request.GetRequestStream().Write(buffer, 0, buffer.Length);
            HttpWebResponse response = (HttpWebResponse)request.GetResponse();
            StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.Default);
            string result = reader.ReadToEnd();
           
            return result;
        }