using System.Collections.Generic;

using System;

using System.Configuration;

​

namespace Simple

{

    public class Program

    {

        public static void Main()

        {

            // Remove this question mark and it will crash  ||

            //                                             _||_

            //                                             \\//

            //                                              \/          

            var x = ConfigurationSettings.AppSettings["Time"]?.ToString();

            Test.start(true);

        }

    }

​

    public class Test

    {

        public static void start(bool g)

        {

            var a = new A(g ? new B() : null);

            var b = new B();

            var x = a.b?.d;

            if ((a.b?.d).HasValue)

            {

                Console.WriteLine("Good");

            }

            else

            {

                Console.WriteLine("Not Good");

            }

        }

    }

    public class A

    {

        public A(B bb)

        {

            b = bb;

        }

​

        public B b

        {

            get;

            set;

        }

    }

​

    public class B

    {

        public B()

        {

            d = DateTime.Now;

        }

​

        public DateTime? d

        {

            get;

            set;

        }

    }

​

}