fatal error unexpectedly found nil while unwrapping an optional value lldb

//  AutoLayout
//
//  Created by Aryan Kashyap on 19/09/2015.
//  Copyright © 2015 Aryan Kashyap. All rights reserved.
//

import UIKit

class ViewController: UIViewController , UIScrollViewDelegate {

    @IBOutlet weak var pageControl: UIPageControl!
    @IBOutlet weak var scrollView: UIScrollView!

    var pageImages : [UIImage!] = []
    var pageViews : [UIImageView?] = []

    override func viewDidLoad() {
        super.viewDidLoad()

        //1

    // The Error shows up on this line 
        pageImages = [UIImage(named:"Asia.png")!,UIImage(named:"Europe.png")!]

        let pageCount = pageImages.count

        //2 
        pageControl.currentPage = 0
        pageControl.numberOfPages = pageCount

        //3
        for _ in 0..<pageCount {
         pageViews.append(nil)
        }

        //4
        let pagesScrollViewSize = scrollView.frame.size
        scrollView.contentSize = CGSizeMake(pagesScrollViewSize.width * CGFloat(pageImages.count), pagesScrollViewSize.height)

        //5
        loadVisiblePages()

    }
    func loadPage(page: Int) {

        if page < 0 || page >= pageImages.count {
            // If it's outside the range of what you have to display, then do nothing
            return
        }

        // 1
        if let _ = pageViews[page] {
            // Do nothing. The view is already loaded.
        } else {
            // 2
            var frame = scrollView.bounds
            frame.origin.x = frame.size.width * CGFloat(page)
            frame.origin.y = 0.0

            // 3
            let newPageView = UIImageView(image: pageImages[page])
            newPageView.contentMode = .ScaleAspectFit
            newPageView.frame = frame
            scrollView.addSubview(newPageView)

            // 4
            pageViews[page] = newPageView
        }
    }

    func purgePage(page: Int) {

        if page < 0 || page >= pageImages.count {
            // If it's outside the range of what you have to display, then do nothing
            return
        }

        // Remove a page from the scroll view and reset the container array
        if let pageView = pageViews[page] {
            pageView.removeFromSuperview()
            pageViews[page] = nil
        }

    }




    func loadVisiblePages() {

        // First, determine which page is currently visible
        let pageWidth = scrollView.frame.size.width
        let page = Int(floor((scrollView.contentOffset.x * 2.0 + pageWidth) / (pageWidth * 2.0)))

        // Update the page control
        pageControl.currentPage = page

        // Work out which pages you want to load
        let firstPage = page - 1
        let lastPage = page + 1


        // Purge anything before the first page
        for var index = 0; index < firstPage; ++index {
            purgePage(index)
        }

        // Load pages in our range
        for var index = firstPage; index <= lastPage; ++index {
            loadPage(index)
        }

        // Purge anything after the last page
        for var index = lastPage+1; index < pageImages.count; ++index {
            purgePage(index)
        }

    }

    func scrollViewDidScroll(scrollView: UIScrollView!) {
        // Load the pages that are now on screen
        loadVisiblePages()
    }

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