Fixes T5770. This error occurs if you run bin/storage upgrade before you set up MySQL credentials.
This isn't what the setup guide says to do, but it's an easy mistake to make and should be a permitted install path since there's no reason you can't do things in this order.
Specifically, we use a mixture of "standard" (configured) and "administrative" (--user and --password) credentials, and if the standard ones are bogus bad things happen. We use the standard credentials to make some initialization order stuff easier, and because there's no --host flag and adding one would be silly, and because we only need administrative credentials to issue ALTER / CREATE statements.