Intercambiador de métodos con Swift 5.5

Estoy intentando sobrescribir el método initWithString en NSURL, he revisado estos problemas/publicaciones anteriores:
– https://stackoverflow.com/questions/46361065/method-swizzling-in-swift-4/46361066#46361066
– https://stackoverflow.com/questions/34317766/how-to-swizzle-init-in-swift
– https://www.uraimo.com/2015/10/23/effective-method-swizzling-with-swift/

He intentado el siguiente código pero no he podido fijar el nuevo método log_initWithString, swiftc no indica nada pero al ejecutarlo obtengo index/index.swift:20: Fatal error: Unexpectedly found nil while unwrapping an Optional value.

import AppKit
import WebKit

let app = NSApplication.shared

//ejemplo: https://github.com/kickstarter/ios-oss/blob/39edeeaefb5cfb26276112e0af5eb6948865cf34/Library/DataSource/UIView-Extensions.swift

private var hasSwizzled = false

extension NSURL {
    public final class func doSwizzle() {
        guard !hasSwizzled else { return }

    hasSwizzled = true

    let original = Selector("initWithString:")
    let swizzled = Selector("log_initWithString:")

    let originalMethod = class_getInstanceMethod(NSURL.self, original)!
    let swizzledMethod = class_getInstanceMethod(NSURL.self, swizzled)!

    let didAddMethod = class_addMethod(NSURL.self, original, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

    if didAddMethod {
        class_replaceMethod(NSURL.self, swizzled, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
    } else {
        method_exchangeImplementations(originalMethod, swizzledMethod)
    }
}

@objc internal func log_initWithString(string URLString: String) {
    NSLog("Hola desde initWithString")

    return log_initWithString(string: URLString)
}


}

class AppDelegate: NSObject, NSApplicationDelegate {
    let window = NSWindow.init(contentRect: NSRect(x: 0, y: 0, width: 750, height: 600), styleMask: [
        NSWindow.StyleMask.titled,
        NSWindow.StyleMask.closable,
        NSWindow.StyleMask.resizable,
        NSWindow.StyleMask.miniaturizable
    ], backing: NSWindow.BackingStoreType.buffered, defer: false)

func applicationDidFinishLaunching(_ notification: Notification) {
    NSURL.doSwizzle()

    let webview = WKWebView(frame: window.contentView!.frame)
    let request = URLRequest(url: URL(string: "https://google.com")!)

    window.contentView?.addSubview(webview)
    webview.load(request)

    window.makeKeyAndOrderFront(nil)
    window.orderFrontRegardless()
    window.center()
}


}

let delegate = AppDelegate()

app.delegate = delegate

app.run()