using System;

​

#nullable enable

​

public class Program

{

    static string? GetString(string? s) => s;

    public static void Main()

    {

        if (GetString("s") is {} f)

            Console.WriteLine("{0} is not null", f);

        if (GetString(null) is {} f2)

            Console.WriteLine("{0} is not null", f2);

    }

}