   }
   
   /// Dismiss `viewController`
-  func dismissSystemViewController(_ viewController: UIViewController, completion: ((Void) -> Void)?) {
+  func dismissSystemViewController(_ viewController: UIViewController, completion: (() -> Void)?) {
     if viewController.modalPresentationStyle == .fullScreen {
       viewController.willMove(toParentViewController: nil)
       removeView(viewController.view)

   - parameter viewController: a view controller to dismiss
   */
  @available(*, deprecated, message: "Use `dismiss(_:completion:)`. This method will be removed soon.")
  public func dismissSystemViewController(_ viewController: UIViewController, completion: ((Void) -> Void)? = nil) {
    dismiss(viewController, completion: completion)
  }


}

/// Root container view controller for System view controllers
@objc(DSLSystemWindowViewController)
private final class SystemWindowViewController: UIViewController {
  typealias Hash = Int
  /// A map from viewController's view hash to it's level
