Can not save new _User object after deleting field value

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.
• I can reproduce the issue with the latest version of Parse Dashboard.

Issue Description

Not able to save or create new objects after deleting one of the field values, using del key after selecting that field cell.

Steps to reproduce

• Click on add new row button
• set value in any field
• select that field and press del key, that should unset that field
• (if any required field, then fill those first) save new row.

Actual Outcome

Can not save new row, getting error You cannot use [object Object] as a query parameter.

Expected Outcome

should be able to save new row.

Pull Request

• PR: #FILL_THIS_OUT

Environment

Dashboard

• Parse Dashboard version: 2.1.0
• Browser (Safari, Chrome, Firefox, Edge, etc.): Chrome
• Browser version: Version 92.0.4515.107 (64-bit)

Server

• Parse Server version: 4.5.0
• Operating system: Ubuntu 20.04.2 LTS
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 3.3
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): remote host

Logs

https://user-images.githubusercontent.com/44117648/127895519-d8cf0bc8-2ff8-49a3-9ee3-8b7bb229afe7.mp4

Start by reproducing the add-new-row flow in Parse Dashboard: enter a value, select the field, press Delete, and save with required fields filled. Trace the new-row save path to identify how the deleted field is represented, then verify that saving succeeds without the query-parameter error.