using System;

public class Program

{

    public static void Main()

    {

        ProvideString("x");

        ProvideString(null);

        ProvideString("asdf");

    }

    static void ProvideString(string statement) =>

        Console.WriteLine(statement switch{

            "x" => "hello x world",

            null => "hello null world",

            _ => statement

        });

}