User authenticated using OAuth not added to default rooms due to default avatar issue

Description:

A new user that perform authentication using OAuth (GitHub, Google, etc.) is not added to rooms configured as "default". A user that register with username and password is added, as expected, to the "default" rooms.

Steps to reproduce:

1. Configure at least one OAuth provider (e.g. GitHub)
2. Create several rooms
3. Add the "default" setting to more than one room
4. Register and login with using OAuth → user is not added to any room but can join them manually
5. Register with email and password → user is added to all default room

Expected behavior:

A new user should be added to all default room not matter the authentication mechanism used.

Actual behavior:

User not added to default room when using OAuth.

Server Setup Information:

• Version of Rocket.Chat Server: 4.6.3 and also reproduce on 4.7.0
• Operating System: Debian GNU/Linux 10 (buster) on the server
• Deployment Method: Docker
• Number of Running Instances: 1
• DB Replicaset Oplog: enabled
• NodeJS Version: v14.18.3
• MongoDB Version: 4.4.13 / wiredTiger (oplog Enabled)

Client Setup Information

• Desktop App or Browser Version: Firefox 91.8.0esr (64 bits)
• Operating System: Debian GNU/Linux 11 (bullseye)

Relevant logs:

{"level":50,"time":"2022-05-09T12:49:50.313Z","pid":37,"hostname":"01a08d797a59","name":"System","msg":"Exception while invoking method setUsername 'Cannot read property 'blob' of undefined'"}

This log is due to code call but I don't know the exact root cause.

Start with apps/meteor/app/lib/server/functions/setUsername.ts at the referenced line and compare the OAuth and username/password registration paths. Reproduce the default-room setup described in the issue while checking the reported 'blob' error. Done means newly registered OAuth users are added to every room marked default, as password-registered users are.