using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

  public static void Main()

  {

    string x = "";

    string y = null;

​

    Console.WriteLine("------");

    Console.WriteLine(x is null);     // null

    Console.WriteLine(!(x is null));  // not null

    Console.WriteLine(x is {});       // not null

    Console.WriteLine("------");

    Console.WriteLine(y is null);     // null

    Console.WriteLine(y is {});       // not null

  }

}