using System;

using System.Collections;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Runtime.Serialization.Formatters;

using System.IO;

using System.Data;

using System.ComponentModel.DataAnnotations;

using System.Globalization;

using System.Reflection;

​

using Newtonsoft.Json;

using Newtonsoft.Json.Linq;

using Newtonsoft.Json.Converters;

using Newtonsoft.Json.Serialization;    

​

using NUnit.Framework; // Throws NUnit.Framework.AssertionException

​

//https://stackoverflow.com/questions/56261012/how-to-serialize-using-json-net-and-ignore-a-nullable-struct-value

​

    public class Entity

    {

        [JsonConverter(typeof(NullJsonConverter))]

        public HasValue<int?> Number { get; set; }

    }

​

    public struct HasValue<T> : IHasValue

    {

        // Had to convert to c# 4.0 syntax for dotnetfiddle

        T m_value;

        public HasValue(T value) { this.m_value = value; }

        public T Value { get { return m_value; } set { m_value = value; } }

        public object GetValue() { return Value; }

    }

​

    internal interface IHasValue

    {

        object GetValue();

    }

​

    public class NullJsonConverter : JsonConverter

    {

        public override bool CanConvert(Type objectType) { throw new NotImplementedException(); }

​

        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)

        {

            var valueType = objectType.GetGenericArguments()[0];

            var valueValue = serializer.Deserialize(reader, valueType);

            return Activator.CreateInstance(objectType, valueValue);

        }

​

        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)

        {

            serializer.Serialize(writer, ((IHasValue)value).GetValue());

        }

    }

​

    class TestClass

    {

        public static void Test()

        {

            int? number = null;

            var settings = new JsonSerializerSettings()

                { 

                    DefaultValueHandling = DefaultValueHandling.Ignore,

                    NullValueHandling = NullValueHandling.Ignore

                };

            var json = JsonConvert.SerializeObject(

                new Entity { Number = new HasValue<int?>(number) },

                settings);

​

            var number2 = JsonConvert.DeserializeObject<Entity>(json, settings).Number.Value;

​

            Console.WriteLine(json);

            Assert.AreEqual(number, number2, "number, number2");

            Assert.AreEqual("{}", json); // Fails because json = {"Number":null}

        }   

        Nullable<HasValue<Nullable<int>>> value = default(HasValue<int?>?);

    }

​

    public class Program

    {

        public static void Main()

        {

            Console.WriteLine("Environment version: " + Environment.Version);

            Console.WriteLine("Json.NET version: " + typeof(JsonSerializer).Assembly.FullName);

            Console.WriteLine();

​

            try

            {

                TestClass.Test();

            }

            catch (Exception ex)

            {

                Console.WriteLine("Failed with unhandled exception: ");

                Console.WriteLine(ex);

                throw;

            }

        }

    }

​