At least when creating a google account, signon-ui isn't able to extract the username from the login page anymore since a couple of months (and newer versions ported to QtWebEngine don't even extract it at all anymore because it was considered to be too fragile, which apparently proved to be true...).
This looks kind of broken, and actually made kio-gdrive useless as that doesn't even list accounts with an empty name.
To fix it, set the name to some arbitrary string in the case that info.userName() is empty.
BUG: 414219
FIXED-IN: 19.12.3