Reference folder not working

I'm getting a question mark near my reference folder. Any idea why this would be happening??

The app builds and then spits out this error "Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value" by bundle.main.url

import UIKit import WebKit class ViewController: UIViewController {

    @IBOutlet weak var loadhtml: WKWebView!

    override func viewDidLoad() {

        super.viewDidLoad()

        let webView = WKWebView()

        let htmlURL = Bundle.main.url(forResource: "index", withExtension: "html", subdirectory: "FILES")!

        webView.loadFileURL(htmlURL, allowingReadAccessTo: htmlURL.deletingLastPathComponent())

        view = webView     }

    override func didReceiveMemoryWarning() {

        super.didReceiveMemoryWarning()

        // dispose of any resources that can be recreated

    }

}