title: How can I change the font of the back button for my navigation bar?
body: <p>How can I change the font of the back button for my navigation bar.</p>
  
  <p>The back button is either "back" or the title from the previous view controller. </p>
  
  <p>I thought this <code>viewDidLoad</code> would work:</p>
  
  <pre><code>navigationController?.navigationItem.leftBarButtonItem?.setTitleTextAttributes([NSFontAttributeName: UIFont(name: "FONTNAME", size: 20)!], forState: UIControlState.Normal)
  </code></pre>
  
  <p>but the <code>leftBarButton?</code> optional returns <code>nil</code>. </p>