using System;   

using System.Dynamic;

using Newtonsoft.Json;

public class Program

{

    public static void Main()

    {

         dynamic sampleObject = new ExpandoObject(); 

        if(1 == 2)

        {

            sampleObject.a = "";

        }

        sampleObject.b = "";

         var test = Newtonsoft.Json.JsonConvert.SerializeObject(sampleObject, new Newtonsoft.Json.JsonSerializerSettings 

        {

          NullValueHandling = NullValueHandling.Ignore,

          DefaultValueHandling = DefaultValueHandling.Ignore

        });

​

        Console.WriteLine(test);

    }

}