ClassCastException when registering ServiceWorker in Safari on MacOS X

[ingosch]

registration = (ServiceWorkerRegistration) object;
in setupRegistration method of ServiceWorkerManager throws a ClassCastException when using Safari on MacOS X.
I think this might be an internal problem with Safari and GWT.

Made a workaround using a native method casting the object.

public native ServiceWorkerRegistration castRegistration(JavaScriptObject o) /*-{
	return o;
}-*/;

protected void setupRegistration() {
	if (isServiceWorkerSupported()) {
		Navigator.serviceWorker.register(getResource()).then(object -> {
			logger.info("Service worker has been successfully registered");
			registration = castRegistration((JavaScriptObject) object);

This works on all systems and browsers I've tested so far.