Newtonsoft.Json.JsonSerializerSettings jSetting = new Newtonsoft.Json.JsonSerializerSettings();
jSetting.NullValueHandling = Newtonsoft.Json.NullValueHandling.Include;
jSetting.DateFormatString = "yyyy-MM-dd HH:mm:ss";
sbContent.Append(JsonConvert.SerializeObject(gameresult,jSetting).Replace(":null,",":\"\",").Replace(":null},":\"\"},"));