[ServiceWorker] ServiceWorkerContainer.controller is prose says to return undefined, but the IDL doesn't allow that (#769)

The IDL says:

    readonly attribute ServiceWorker? controller;

and undefined is not a valid `ServiceWorker?` value.

What you would probably want is for the property to not exist in a secure context at all, right?

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Reply to this email directly or view it on GitHub:
https://github.com/slightlyoff/ServiceWorker/issues/769