致命错误：展开一个可选值时意外发现nil

Question

import UIKit

import WebKit

class ViewControllerMaps: UIViewController, WKUIDelegate  {

@IBOutlet weak var ActvityView: UIActivityIndicatorView!
@IBOutlet weak var Videoview: WKWebView!{
    didSet {
        webView.uiDelegate = self
        webView.navigationDelegate = self as? WKNavigationDelegate
    }
}

var webView: WKWebView!

override func loadView() {
    let webConfiguration = WKWebViewConfiguration()
    webView = WKWebView(frame: .zero, configuration: webConfiguration)
    webView.uiDelegate = self
    view = webView
}
override func viewDidLoad() {
    super.viewDidLoad()

    let myURL = URL(string:"//twitter.com/")
    let myRequest = URLRequest(url: myURL!)
    Videoview.load(myRequest) // ERROR OCCURS HERE  

}

    func webViewDidStartLoad(_  : WKWebView)  {
        ActvityView.startAnimating()
        NSLog("The webview is started loading")
    }
    func webViewDidStopLoad(_  : WKWebView)  {
        ActvityView.stopAnimating()
        NSLog("The webview is done loading")

    }

    func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) {
        DispatchQueue.main.async {
            self.ActvityView.stopAnimating()
            NSLog("The Webview Has finish Navigating")

        }

}
override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

   }

如何阻止可选的nil值出现？我已经注释了他在哪里编写了发生错误的脚本，但是我不确定如何确切地解决它。

X-Code的版本为9.4.1

WKWebview的其他信息委托给它链接到的ViewController。

谢谢：）