using System;

public class Program

{

    #nullable enable

    static void PrintUpper(string? text)

    {

        if (text is not null) 

            Console.WriteLine(text.ToUpper());

    }   

    public static string IsNull(string? value)

    {

        if (value != null)

        {

            return value;

        }

        return "null";

    }

    public static void Main()

    {

        PrintUpper("Hello World");

        Console.WriteLine(IsNull("GG"));

    }

}