Any idea why the Alert Box is not displaying? Interactive App! Any feedback highly appreciate it!!! Thanks in advance!!

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.
}

//..Preparing the segue... when the segue is about to fire..
//..the segue object and the sender two arguments.. 
override func prepare(for segue: UIStoryboardSegue, sender: Any?)
{
    if segue.identifier == "startAdventure"
    {
        //..Checking if a name has been provided..
        do {
          if let name = nameTextField.text {
            if name == " "
            {
                //..Thrworing error..
                throw AdventureError.nameNotProvided
             }
            else
            {
                guard let pageController = segue.destination as? PageController
                else
                {
                    return;
                }
                pageController.page = Adventure.story(withName: name)
            }
        }
    }
    //..Handling the error..
    catch AdventureError.nameNotProvided
    {
        //.Displayiing the alet message, you haven't provided a name..
        let alertController = UIAlertController(title: "Name haven't been provided", message: "Provided a name", preferredStyle: .alert )

        let action = UIAlertAction (title: "OK", style: .default, handler: nil )
        //..Adding action to the alertController variable..
        alertController.addAction(action)

        //.Presenting that to the ViewController..
       present(alertController, animated: true, completion: nil)    
    }
    catch let error
    {
            //..Throwing error on purpose.., 
            fatalError("\(error.localizedDescription)")
    }
  }