certain users can only be deleted with erase: false

Description

I was purging a few thousand users an appbridge left behind, all with { "erase": true }, but got {"errcode":"M_UNKNOWN","error":"No row found (profiles)"} for a few dozen of them. Without erase: true, I could successfully deactivate them.

Steps to reproduce

• Try to delete users with erase: true
• Observe failure
• Try to delete same users without erase: true
• Observe success

Version information

• Homeserver: synapse @ helsinki-systems.de
• Version: {"server_version":"1.36.0","python_version":"3.8.9"}
• Install method: NixOS module
• Platform: NixOS 21.05

[dklimpel]

If you try to deactivate a user with { "erase": true }. Synapse try to unset avatar_url and displayname in profile table. If your user has no profile, it goes wrong. One solution is that set_avatar_url and set_displayname or the DeactivateAccountHandler have to catch this exception.

[ajs124]

Not sure. I think in my case it might have been matrix-appservice-irc somehow screwing up? Although the users not having displaynames would also explain issues I was seeing when using it, at the time. Namely, those (bridged) users being displayed with their matrix ID(?) instead of a proper name.