title: How to check existence of the controller in the storyboard before to instantiate it?
body: <p>When working with storoboard through code we can instantiate controllers via identifier, but if the controller with this identifier is not found will be crash. How I can avoid crashes and/or check existence of the controller in advance?</p>
  
  <p>Controller instantiate example:</p>
  
  <pre><code>UIViewController *controller = [[UIStoryboard storyboardWithName:@"Settings" bundle:nil] instantiateViewControllerWithIdentifier:model.identifier];
  [self.navigationController pushViewController:controller animated:YES];
  </code></pre>