using System;

public class Program

{

    public static void Main()

    {

        var test = new Test

        {

            Test1 = null

        };

​

        if(test.Test1.HasValue)

            Console.WriteLine(test.Test1.Value);

        else

            test.Test1 = 123;

        if(test.Test1.HasValue)

            Console.WriteLine(test.Test1.Value);

        else

            throw new Exception("aj aj aj");

    }

}

public class Test

{

    public int? Test1 { get; set; }

​

}

​