using System;

using System.Linq;                  

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

            int?[]emptyList = {1, 2};

​

            var newList1 = emptyList.DefaultIfEmpty(); 

            var newList2 = emptyList.DefaultIfEmpty(-1);

            var hej = newList2.FirstOrDefault(x => x == 10);

            Console.WriteLine("Hej: " + hej);

    }

}