using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        var listOfThings = new List<string> { "String one" };

​

        if (listOfThings?.Count != 0)

        {

            Console.WriteLine("Not null and has items");

        }

​

        listOfThings = null;

​

        if (listOfThings?.Count != 0)

        {

            Console.WriteLine("This check will give you a false positive since a null object has no count.");

            Console.WriteLine("If you then assume there are items and try to operate on listOfThings, you will get a NullReferenceException.");

            // foreach (var thing in listOfThings) { ... } <- this will blow up

        }

​

        if (listOfThings is null || listOfThings.Count == 0)

        {

            Console.WriteLine("Null or empty with correct check using pre C# 9 syntax.");

        }

​

        listOfThings = new List<string>();

​

        if (listOfThings is null || listOfThings.Count == 0)

        {

            Console.WriteLine("Null or empty second check.");

        }

    }

}