using System;

public class Program

{

    public class MyD {

        public DateTime? D { get; set;}

    }

    public static void Main()

    {

        MyD a = null;

        MyD b = new MyD();

        MyD c = new MyD {

            D = DateTime.Now

        };

        Console.WriteLine(a?.D.GetValueOrDefault() != default(DateTime) ? a?.D.Value.Year : string.Empty);

        Console.WriteLine(b?.D.GetValueOrDefault() != default(DateTime) ? b?.D.Value.Year : string.Empty);

        Console.WriteLine(c?.D.GetValueOrDefault() != default(DateTime) ? c?.D.Value.Year : string.Empty);      

    }

}