.Net Core 统一全局处理字符串为Null问题

services.AddControllersWithViews().AddNewtonsoftJson(options =>
            {
                //设置序列化时间格式
                options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss";
                  
                options.SerializerSettings.ContractResolver = new NullToEmptyStringResolver(); 
            });

public class NullToEmptyStringResolver : DefaultContractResolver
    { 
        protected override JsonConverter ResolveContractConverter(Type objectType)
        {
            if (objectType == typeof(long))
            {
                return new JsonConverterLong();
            }

            if (objectType == typeof(int))
            {
                return new JsonConverterInt();
            }

            if (objectType == typeof(decimal))
            {
                return new JsonConverterDecimal();
            }

            if (objectType == typeof(double))
            {
                return new JsonConverterDouble();
            }

            return base.ResolveContractConverter(objectType);
        }

        protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
        {
            return type.GetProperties().Select(c =>
            {
                var jsonProperty = base.CreateProperty(c, memberSerialization);
                jsonProperty.ValueProvider = new NullToEmptyStringValueProvider(c);
                return jsonProperty;
            }).ToList();
        }
    }

    public class NullToEmptyStringValueProvider : IValueProvider
    {
        private readonly PropertyInfo _memberInfo;

        public NullToEmptyStringValueProvider(PropertyInfo memberInfo)
        {
            _memberInfo = memberInfo;
        }

        public object GetValue(object target)
        {
            var result = _memberInfo.GetValue(target);
            if (_memberInfo.PropertyType == typeof(string) && result == null)
                result = string.Empty;
            return result;
        }

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