using System;

using System.Collections.Generic;

using System.Linq;

public class Programx

{

    public class testClass

    {

        public int num;

    }

    public static void Main()

    {

//      List<testClass> tests = new List<testClass>();

        List<testClass> tests = null;

        testClass t = new testClass();

        t.num = 0;

//      tests?.Add(t);

​

        tests

            ?.Where(test => test.num == 1)

           .Select(test => new testClass())

            .ToList();

        Console.WriteLine($"test: {tests?.Count ?? 0}");

    }

}