workbox: Safari bug

Library Affected: workbox-sw, workbox-build, etc.?

Browser & Platform: Safari 12 macOS High Sierra 10.13.6

Issue or Feature Request Description: Refreshing workbox PWAs (like https://material-ui.com) leads to this sometimes.

Safari cannot open the page. The error was: "FetchEvent.respondWith received an error: Returned response is null. (WebKitServiceWorker: 0)"

Console has:

Failed to load resource: bad URL safari-resource:/page-load-errors-extras.css

Confirmed that they work fine on Firefox, Chrome and private mode Safari.

I figured if I cleared the cache, it would help, but it doesn’t seem to kill the service workers. Workaround is to disable service workers in Developer mode and I can load the websites properly.