using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(string.IsNullOrWhiteSpace(null)); // true

        Console.WriteLine(string.IsNullOrWhiteSpace(string.Empty)); // true

        Console.WriteLine(string.IsNullOrWhiteSpace("      ")); // true

        Console.WriteLine(string.IsNullOrWhiteSpace("      a")); // false

    }

}