`authData` is reset on save for newly created anonymous user

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

authData is reset for newly created anonymous users, if I just save it right after creating.

Steps to reproduce

To reproduce the issue use this cloud code. It's minimal artificial example, but it shows the problem:

const user = await Parse.AnonymousUtils.logIn()
await user.save(null, { useMasterKey: true })

But there is workaround to keep authData in place:

const user = await Parse.AnonymousUtils.logIn()
await user.save('authData', {}, { useMasterKey: true })

in this case it's not overwritten by empty object, and keeps original value.

Actual Outcome

authData should be saved to DB

Expected Outcome

authData is undefined in DB

Failing Test Case / Pull Request

• 🤩 I submitted a PR with a fix and a test case.
• 🧐 I submitted a PR with a failing test case.

Environment

Server

• Parse Server version: 4.5.0
• Operating system: OS X Bug Sur 11.2.1
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local and remote Heroku

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 4.4.6
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): MongoDB Atlas

Client

• SDK (iOS, Android, JavaScript, PHP, Unity, etc): JavaScript
• SDK version: 2.17.0

Logs

no logs

Start by reproducing the issue with Parse.AnonymousUtils.logIn followed by user.save(null, { useMasterKey: true }), then compare it with the workaround that explicitly saves authData. Trace how the Parse Server save path handles authData for newly created anonymous users; done means the original authData remains persisted after the immediate save.