using System;

​

public class Program

{

    public static void Main()

    {

        string str = null;

        Console.WriteLine(str.GetValueOrDefault("hi"));

        Console.WriteLine("done");

    }

}

​

public static class DERPS

{

    public static string GetValueOrDefault(this string str, string defaultString)

    {

        return !string.IsNullOrEmpty(str) ? str : defaultString;

    }

}