using System;

using System.Collections.Generic;

using System.Linq;

using System.Reflection;

using Newtonsoft.Json;

using Newtonsoft.Json.Serialization;

public class Program

{

    public static void Main()

    {

        JsonSerializerSettings settings = new JsonSerializerSettings();

        settings.ContractResolver = new NullToEmptyListResolver();

        settings.ObjectCreationHandling = ObjectCreationHandling.Replace;

        settings.Formatting = Formatting.Indented;

​

        Console.WriteLine("Serializing object with null lists...");

        Foo foo = new Foo();

        string json = JsonConvert.SerializeObject(foo, settings);

        Console.WriteLine(json);

        Console.WriteLine();

        Console.WriteLine("Deserializing back to objects...");

        foo = JsonConvert.DeserializeObject<Foo>(json, settings);

        Console.WriteLine("IntList size: " + foo.IntList.Count);

        Console.WriteLine("StringList size: " + foo.StringList.Count);

        Console.WriteLine();

​

        Console.WriteLine("Deserializing JSON with null lists...");

        json = @"{ ""IntList"" : null, ""StringList"" : null }";

        foo = JsonConvert.DeserializeObject<Foo>(json, settings);

        Console.WriteLine("IntList size: " + foo.IntList.Count);

        Console.WriteLine("StringList size: " + foo.StringList.Count);

        Console.WriteLine();

        Console.WriteLine("Serializing back to JSON...");

        json = JsonConvert.SerializeObject(foo, settings);

        Console.WriteLine(json);

        Console.WriteLine();

​

        Console.WriteLine("Serializing object with non-empty lists...");

        foo = new Foo

        {

            IntList = new List<int> { 1, 2, 3 },

            StringList = new List<string> { "a", "b", "c" }

        };

        json = JsonConvert.SerializeObject(foo, settings);

        Console.WriteLine(json);

        Console.WriteLine();

        Console.WriteLine("Deserializing back to objects...");

        foo = JsonConvert.DeserializeObject<Foo>(json, settings);

        Console.WriteLine("IntList: " + string.Join(", ", foo.IntList.Select(i => i.ToString())));

        Console.WriteLine("StringList: " + string.Join(", ", foo.StringList.Select(s => s)));

        Console.WriteLine();

    }

}

​

class Foo

{

    public List<int> IntList { get; set; }

    public List<string> StringList { get; set; }

}

​

class NullToEmptyListResolver : DefaultContractResolver

{

    protected override IValueProvider CreateMemberValueProvider(MemberInfo member)

    {

        IValueProvider provider = base.CreateMemberValueProvider(member);

​

        if (member.MemberType == MemberTypes.Property)

        {

            Type propType = ((PropertyInfo)member).PropertyType;

            if (propType.IsGenericType &&

                propType.GetGenericTypeDefinition() == typeof(List<>))

            {

                return new EmptyListValueProvider(provider, propType);

            }

        }

​

        return provider;

    }

​

    class EmptyListValueProvider : IValueProvider

    {

        private IValueProvider innerProvider;

        private object defaultValue;

​

        public EmptyListValueProvider(IValueProvider innerProvider, Type listType)

        {

            this.innerProvider = innerProvider;

            defaultValue = Activator.CreateInstance(listType);

        }

​

        public void SetValue(object target, object value)

        {

            innerProvider.SetValue(target, value ?? defaultValue);

        }

​

        public object GetValue(object target)

        {

            return innerProvider.GetValue(target) ?? defaultValue;

        }

    }

}

​