Property 'self.menuViewController' not initialized at super.init call

I'm running into this error on a viewController and not sure why it's happening. The controller is currently set up like this:

class ContainerViewController: UIViewController {

  init(sideMenu: UIViewController, center: UIViewController) {
    menuViewController = sideMenu
    centerViewController = center
    super.init(nibName: nil, bundle: nil)
  }

  required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)// This is where the error happens
  }

}

Any clue why this may be happening?