title: UINavigationController: initWithRootViewController: returning nil
body: <p>I am trying to setup a Navigation Controller for the first time and it is consistently returning nil, even though I can directly set the view controller to the window and all is well.
  The code from the App Delegate is pretty standard:</p>
  
  <pre><code>//  Set the root view controller and display the window
  _vcMain = [ [ ViewControllerMain alloc ] initWithNibName: nil bundle: nil ];
  self.navController = [ [ UINavigationController alloc ] initWithRootViewController: _vcMain ];
  
  //  self.window.rootViewController = _vcMain;  &lt;-- Works
  self.window.rootViewController = _navController;
  [self.window makeKeyAndVisible];
  
  return( YES );
  </code></pre>
  
  <p>ViewControllerMain is a subclass of UIViewController.</p>
  
  <p>Is there a way of getting an error about what went wrong with the initialisation?  Any help would be appreciated as this shouldn't really be causing any issues  :-(</p>