   // MARK: - Animations
 
   func moveControllerViews(down: Bool) {
-    guard let visibleController = navigationController.visibleViewController
+    guard let navigationController = self.navigationController,
+        visibleController = navigationController.visibleViewController
       where Config.modifyInset
       else { return }
 

    static let totalDelay: NSTimeInterval = popUp + movement * 2
  }

  var navigationController = UINavigationController()
  var edgeInsetHeight: CGFloat = 0
  var whisperView: WhisperView!
  var delayTimer = NSTimer()

  }

  func silentWhisper(controller: UINavigationController, after: NSTimeInterval) {
    self.navigationController = controller
    guard let navigationController = self.navigationController else { return }
    
    var whisperSubview: WhisperView? = nil
    for subview in navigationController.navigationBar.subviews {
      if let whisper = subview as? WhisperView {
