public class Foo
{
    public int Prop1;
    [DefaultValue("")]
    public string Prop2;
    public int? Prop3;
    public Bar Prop4;
    public Bar[] Prop5;
};

public class Bar
{
    public int Prop1;
    public string Prop2;
    public int? Prop3;
};

public void NullOrEmptyStringTerminator()
{
    var bar = new Bar { Prop1 = 0, Prop2 = "", Prop3 = 0 };
    var bar2 = new Bar { Prop1 = 0, Prop3 = 0 };

    var inputs = new[] {
       new Foo{ Prop1= 1, Prop2="", Prop4= bar, Prop5 = new []{bar,bar,bar} },
       new Foo{ Prop1= 1, Prop4= bar, Prop5 = new []{bar2,bar2,bar2} },
    };

    var jsonResults =
            inputs
                .Select(x =>
                    new
                    {
                        Item = x,
                        NormalSerialisation =
                            JsonConvert.SerializeObject(
                                x,
                                Formatting.Indented,
                                new JsonSerializerSettings { }
                            ),
                        CustomSerialisation =
                             JsonConvert.SerializeObject(
                                x,
                                Formatting.Indented,
                                new JsonSerializerSettings
                                {
                                    NullValueHandling = NullValueHandling.Ignore,
                                    DefaultValueHandling = DefaultValueHandling.Ignore,
                                })
                    }
                ).ToList();
}

using System;
using System.Linq;
using System.Collections.Generic;
using System.ComponentModel;
using Newtonsoft.Json;

public class Program
{
    public static void Main()
    {
        var inputs = new List<object>()
        {new Foo{Prop2 = "" , Bar = new Bar()}};
        foreach (object input in inputs)
        {
            string NormalSerialisation = JsonConvert.SerializeObject(input, Formatting.Indented, new JsonSerializerSettings{});
            string CustomSerialisation = JsonConvert.SerializeObject(input, Formatting.Indented, new JsonSerializerSettings{NullValueHandling = NullValueHandling.Ignore, DefaultValueHandling = DefaultValueHandling.Ignore});
            Console.WriteLine("normal:");
            Console.WriteLine(NormalSerialisation);
            Console.WriteLine("custom:");
            Console.WriteLine(CustomSerialisation);
        }
    }

    public class Foo
    {

        public string Prop2
        {
            get;
            set;
        }

        public Bar Bar
        {
            get;
            set;
        }
    }

    public class Bar
    {
        [DefaultValue("")]
        public string Prop2;
    }
}

normal:
{
  "Prop2": "",
  "Bar": {
    "Prop2": null
  }
}
custom:
{
  "Prop2": "",
  "Bar": {}
}