JsonConvert.SerializeObject 空值处理

var settings = new JsonSerializerSettings() { ContractResolver= new NullToEmptyStringResolver() };
var str = JsonConvert.SerializeObject(yourObj, settings);

    public class NullToEmptyStringResolver : Newtonsoft.Json.Serialization.DefaultContractResolver
    {
        protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
        {
            return type.GetProperties()
                    .Select(p =>
                    {
                        var jp = base.CreateProperty(p, memberSerialization);
                        jp.ValueProvider = new NullToEmptyStringValueProvider(p);
                        return jp;
                    }).ToList();
        }
    }

    public class NullToEmptyStringValueProvider : IValueProvider
    {
        PropertyInfo _MemberInfo;
        public NullToEmptyStringValueProvider(PropertyInfo memberInfo)
        {
            _MemberInfo = memberInfo;
        }

        public object GetValue(object target)
        {
            object result = _MemberInfo.GetValue(target, null);
            if (_MemberInfo.PropertyType == typeof(string) && result == null) result = "";
            return result;

        }

        public void SetValue(object target, object value)
        {
            _MemberInfo.SetValue(target, value,null);
        }
    }