using System;

public class Program

{

    public static void Main()

    {

        // IsNullOrEmpty() is equivalent to: s == null || s == String.Empty;

        string strA = null;

        string strB = String.Empty;

        string strC = "Pirzada";

        string strD = "";

​

        Console.WriteLine(check(strA)); // True

        Console.WriteLine(check(strB)); // True

        Console.WriteLine(check(strC)); // False

        Console.WriteLine(check(strD)); // True

​

    }

    public static bool check(string str) 

    { 

        return String.IsNullOrEmpty(str);

    }

}