问Swift prefersLargeTitles在加载WKWebview时崩溃

EN

class NavigationController: UINavigationController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let appearance = UIBarButtonItem.appearance()
        appearance.setBackButtonTitlePositionAdjustment(UIOffset.init(horizontal: 0.0, vertical: -60), for: .default)

        self.navigationBar.barTintColor = UIColor.white
        self.navigationBar.prefersLargeTitles = true
        self.navigationBar.isTranslucent = true
        self.navigationBar.tintColor = UIColor.black
    }
}

class resultViewController: UIViewController
{
    private var webView: WKWebView!

    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.backgroundColor = UIColor.white

        webView = WKWebView(frame: CGRect(x: 0, y: 0, width: self.view.frame.size.width, height: self.view.frame.size.height))
        webView.navigationDelegate = self
        webView.scrollView.delegate = self
        self.view.addSubview(webView)
        let url = URL(string: "https://google.com")
        webView.load(URLRequest(url: url!))
    }

}