1. 定义一个自定义的JsonConverter类，用于控制反序列化过程中的类型转换。

将null值转换为空字符串的自定义转换器：

 public class EmptyStringConverter : JsonConverter
        {
            public override bool CanConvert(Type objectType)
            {
                return objectType == typeof(string);
            }
            public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
            {
                if (reader.TokenType == JsonToken.Null)
                {
                    return string.Empty;
                }
                else
                {
                    return reader.Value;
                }
            }
            public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
            {
                throw new NotImplementedException();
            }
        }

2.使用JsonSerializerSettings对象设置反序列化

 public class JsonHelper
    {
        /// <summary>
        /// 从json串解析指定类型
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="content"></param>
        /// <returns></returns>
        public static T FromJsonString<T>(string content)
        {
            var settings = new JsonSerializerSettings();
            settings.Converters.Add(new EmptyStringConverter());
            return JsonConvert.DeserializeObject<T>(content, settings);
            //转换的是值类型可以将这些属性或字段声明为可空类型（int?,double?等或者使用默认值来代替null）
            //return JsonConvert.DeserializeObject<T>(content);
        }


        /// <summary>
        /// 将对象转换为json字符串
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="data"></param>
        /// <param name="formatting">是否格式化输出</param>
        /// <returns></returns>
        public static string ToJson<T>(T data, bool formatting = false)
        {
            return JsonConvert.SerializeObject(data, formatting ? Formatting.Indented: Formatting.None);
        }

    }