响应总是null, restsharp

我对post数据使用restsharp，然后在post完成后返回一些单个值，但它的响应总是得到null。

public static IRestResponse Services(Object obj)
    {
        var client = new RestClient("http://192.168.1.5/OpManWeb.ServiceHost/api");
            var request = new RestRequest("/SaveExternalOrder/", Method.POST);
            var json = JsonConvert.SerializeObject(obj, Formatting.None,
                new JsonSerializerSettings()
                {
                    ReferenceLoopHandling = ReferenceLoopHandling.Ignore
                });
            request.AddParameter("text/json", json, ParameterType.RequestBody);
            var response = client.Execute(request);
            return response;
    }