using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var listA = new List<string>()

        {

            "Test"

        };

        List<string> listB = null;

        var listC = listA.Intersect(listB);

        Console.WriteLine(string.Join(",", listC));

    }

}