Specifically, botsin.space (for sure) returns a display name of `""`. Since that's not meaningful, I just added a check to replace the display name with the username if the display name is empty.
I didn't want to do this unless we had to but Mastodon is introducing requirming
signed requests soon, so even if a user doesn't use bitbot as an instance, we'll
still need to be able to serve Actor (and key) over the REST API