using System;

using System.Threading.Tasks;

using System.Collections.Generic;

using System.Linq;

​

namespace ConsoleApp

{

    class Program

    {

        static async Task Main(string[] args)

        {

            var t1 = new List<string?>()

            {

                null, 

                "hello", 

                "world"

            };

            var a = t1.First();

            if (a == null)

            {

                Console.WriteLine("first element is null");

            }

​

            Console.WriteLine("Finish");

        }

    }

}