title: self.navigationController?.popViewControllerAnimated from UIAlertController
body: <p>I'm new to swift but I think I'm getting a hang of it. This stumped my progress pretty hard though.</p>
  
  <p>What I want to do is to throw an error message to the user when we can't find relevant data to his query, and then proceed to take him back to the previous ViewController.</p>
  
  <p>However, I'm having real trouble doing this. On the line where I add the action I get the following error: 'UIViewController?' is not a subtype of Void</p>
  
  <pre><code>let alertController = UIAlertController(title: "Oops", message: "We couldn't find any data for this title, sorry!", preferredStyle: UIAlertControllerStyle.Alert)
  
  alertController.addAction(UIAlertAction(title: "Ok", style: .Default, handler: { action in
      self.navigationController?.popViewControllerAnimated(true)   
  }))
  </code></pre>
  
  <p>How do I do this? Am I missing something obvious? I tried messing around with the deprecated UIAlertView but became none the wiser.</p>