DOi is not discarded from the PID table if removed without replacing

[sakshamarora1]

Package version (if known): latest

Steps to Reproduce

1. Publish a record with an external DOI.
2. Edit and remove DOI, re-publish.
3. Create a new record and re-use the same DOI and save
4. See error 'already exists'

On the other hand, if you replace the DOI with a new one, it will remove the old one from the PID table.

Expected behavior

The DOI should be made available for re-use once it is deleted (without replacement) from a record.

[github-actions]

This issue was automatically marked as stale.