Null Object Pattern in Swift

ViewController.swift

//
//  ViewController.swift
//  NullObject
//
//  Created by Suprie on 1/18/16.
//  Copyright © 2016 Suprie. All rights reserved.
//

import UIKit


protocol StationProtocol {
    var id: Int { set get }
    var name: String { set get }
    var isEmpty: Bool { set get }
}

class EmptyStation : StationProtocol {
    var id   = -1
    var name = ""
    var isEmpty = true
}

class Station : StationProtocol {
    var id = 0
    var name = ""
    var isEmpty = false
    
    init(id: Int, name: String){
        self.id = id
        self.name = name
    }
}

class Video {
    static let nullVideo: NullVideo = NullVideo()
    
    var id: Int
    var title: String
    
    init(id: Int, title: String) {
        self.id = id
        self.title = title
    }
}

class NullVideo: Video {
    
    convenience init() {
        self.init(id: -1, title: "")
    }
    
}

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func NotNillTapped(sender: AnyObject) {
        let station = Station(id: 1, name: "Tanah abang")
        processStation(station)
    }

    @IBAction func NilTapped(sender: AnyObject) {
        let emptyStation = EmptyStation()
        processStation(emptyStation)
    }
    
    @IBAction func vidioNotNilTapped(sender: AnyObject) {
        let video = Video(id: 1, title: "Haloha")
        processVideo(video)
    }
    
    @IBAction func vidioNilTapped(sender: AnyObject) {
        processVideo(Video.nullVideo)
    }
    
    func processStation(station: Station) {
        let alert = UIAlertController(title: "Yay", message: "Object is not null", preferredStyle: .Alert)
        alert.addAction(UIAlertAction(title: "Ummm, Okay", style: .Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
    
    func processStation(station: EmptyStation) {
        let alert = UIAlertController(title: ":(", message: "Object is null", preferredStyle: .Alert)
        alert.addAction(UIAlertAction(title: "Ummm, Okay", style: .Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
    
    
    func processVideo(video: Video) {
        let alert = UIAlertController(title: "Yay", message: "Object is not null", preferredStyle: .Alert)
        alert.addAction(UIAlertAction(title: "Ummm, Okay", style: .Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
    
    func processVideo(video: NullVideo) {
        let alert = UIAlertController(title: ":(", message: "Object is  null", preferredStyle: .Alert)
        alert.addAction(UIAlertAction(title: "Ummm, Okay", style: .Default, handler: nil))
        self.presentViewController(alert, animated: true, completion: nil)
    }
 
}