WEBブラウザ構築

swiftでWEBブラウザを作成しているのですが、Thread1 :signal SIGABRTが解消されません。。。！

下記にソースを記載致します。
お判りになる方いらっしゃいましたらご教授お願い致します。

import UIKit

class ViewController: UIViewController, UIWebViewDelegate {
    @IBOutlet weak var textField: UITextField!
    @IBOutlet weak var webView: UIWebView!
    @IBOutlet weak var backButton: UIBarButtonItem!
    @IBOutlet weak var forwardButton: UIBarButtonItem!
    @IBOutlet weak var activityIndicatorView: UIActivityIndicatorView!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        self.webView.delegate = self
        
        // Do any additional setup after loading the view, typically from a nib.
        let startUrl = "http://dotinstall.com"
        if let url = NSURL(string: startUrl){
            let urlRequest = NSURLRequest(URL: url)
            self.webView.loadRequest(urlRequest)
        }
        
        self.setupButtonsEnabled()
        self.activityIndicatorView.hidesWhenStopped = true
        
    }
    
    func setupButtonsEnabled(){
        self.backButton.enabled = self.webView.canGoBack
        self.forwardButton.enabled = self.webView.canGoForward

    }
    
    func webViewDidStartLoad(webView: UIWebView) {
        self.activityIndicatorView.startAnimating()
    }
    
    func webViewDidFinishLoad(webView: UIWebView) {
        self.activityIndicatorView.stopAnimating()
        self.setupButtonsEnabled()
    }
    
        

    

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    
        }
    
    @IBAction func goBack(sender: AnyObject) {
        self.webView.goBack()
    }
    @IBAction func goForward(sender: AnyObject) {
        self.webView.goForward()
    }
    @IBAction func reload(sender: AnyObject) {
        self.webView.reload()
    }

}