It's impossible to have full-disk encryption with that config, right? (i.e., does FileVault work for the root user?)
If you can get in from an install CD, you can reset passwords as needed.
If I were writing this patch, I'd probably check to see if the root user's password was indeed blank, but given that use of the root account only is extremely unsupported I cannot get too upset about Apple breaking that use case as long as you can get back in.
The issue wasn’t actually specific to a blank password. You could try to log in as root using any password, and as long as root had never had a password set, it would fail but set root’s password to whatever you entered.
If you can get in from an install CD, you can reset passwords as needed.
If I were writing this patch, I'd probably check to see if the root user's password was indeed blank, but given that use of the root account only is extremely unsupported I cannot get too upset about Apple breaking that use case as long as you can get back in.