I don't know it this is expected. However, the repository is not empty any more and the error is gone as well.
Reproduced the result and is consistent with yours. I'm no longer facing the issue so I'm guessing you're right: it's related to the repository emptiness. We can close the thread safely. As for the discussion of apt expectation, it's best to open a separate thread in the appropriate mailing list.
Thanks all for your support! =)
Regards,
Holloway