Sometimes a player's username gets displayed as "null" for some reason in the Arena/in-game

[AlexNisnevich]

see https://discord.com/channels/301800217055985665/1107067582940455052/1107067647541125182

Note that in #log, this game was registered as being played by null:

:crossed_swords: Game 'everything!' played between optionboom and null (format: Everything Draft)

but when it was stored in Firebase, it got stored with a real user ID, albeit one for a user that doesn't seem to exist: