e0ed59e55f
Requests from clients that are not assigned a client ID by the browser
will produce `fetch` events with `null` or empty (`''`) `clientId`s.
Previously, the ServiceWorker only handled `null` values correctly. Yet
empty strings are also valid (see for example [here][1] and [there][2]).
With this commit, the SW will interpret _all_ falsy `clientId` values
the same (i.e. "no client ID assigned") and handle them appropriately.
Related Chromium issue/discussion: [#832105][3]
[1]: 4cc72bd0f1/docs/index.bs (L1392)
[2]: https://w3c.github.io/ServiceWorker/#fetchevent-interface
[3]: https://bugs.chromium.org/p/chromium/issues/detail?id=832105
Fixes #23526
PR Close #23625