I'm getting a fatal error: unexpectedly found nil while unwrapping an optional value

import Foundation
import UIKit

class ViewController2: UIViewController {

    @IBOutlet weak var goBackToFirstViewController: UIButton!
    @IBOutlet weak var globeMap: UIImageView!
    @IBOutlet weak var displayInfoHeader: UILabel!
    @IBOutlet weak var button: UIButton!
    @IBOutlet weak var animateImageView: UIButton!

    var imageList = [UIImage]()

    @IBAction func animateAction() {
        startAnimation()
    }

    @IBAction func hideAll(sender: AnyObject) {
        displayInfoHeader.hidden = true
        button.hidden = true
    }

    @IBAction func singaporeInformation(sender: AnyObject) {
        button.hidden = false
        displayInfoHeader.hidden = false
        displayInfoHeader.text = "Singapore, Singapore"
    }

    @IBAction func boiseInformation(sender: AnyObject) {
        button.hidden = false
        displayInfoHeader.hidden = false
        displayInfoHeader.text = "Boise, Idaho"
    }

    @IBAction func indiaInformation(sender: AnyObject) {
        button.hidden = false
        displayInfoHeader.hidden = false
        displayInfoHeader.text = "Mumbai, India"
    }

    @IBAction func paloAltoInformation(sender: AnyObject) {
        button.hidden = false
        displayInfoHeader.hidden = false
        displayInfoHeader.text = "Palo Alto, California"
    }

    override func viewDidLoad() {

        for i in 1...53 {
            let imageName = "\(i).png"
            imageList.append(UIImage(named: imageName)!) //THIS IS WHERE I AM GETTING MY ISSUE
        }

        button.hidden = true
        displayInfoHeader.hidden = true
        globeMap.image = UIImage(named: "map.png")
        super.viewDidLoad()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

    func startAnimation() -> Void {
        if !globeMap.isAnimating() {
            globeMap.animationImages = imageList
            globeMap.startAnimating()
        } else {
            globeMap.stopAnimating()
            globeMap.image = UIImage(named: "map.png")
        }

    }
}