Another issue from exception telemetry. If for any reason we can't iterate the XPI staging directory, XPIProvider.jsm:getDirectoryEntries() returns null (and doesn't close its directory enumerator), but none of the callers check for null.
Created attachment 8394329 [details] [diff] [review]
Don't return null from getDirectoryEntries
(I was wrong about not closing the iterator, though we did try to close it even if we fail to get one)
Rather than spread the null check around to all the callers, I just return an empty array, since there's not much interesting the callers could do with knowledge of the failure.