Backend returns null in DestructionListItemReview for the zaak field [Backend/Frontend]

[SilviaAmAm]

https://dimpact.atlassian.net/jira/software/c/projects/PZ/boards/258/backlog?selectedIssue=PZ-3969

The backend returns null if the zaak has been deleted. (https://github.com/maykinmedia/open-archiefbeheer/blob/main/backend/src/openarchiefbeheer/destruction/api/serializers.py#L473)

The helptext says differently: https://github.com/maykinmedia/open-archiefbeheer/blob/main/backend/src/openarchiefbeheer/destruction/api/serializers.py#L459

The api docs also need fixing because they don't say that the zaak field can be null.

Frontend needs fixing because it doesn't handle a zaak being deleted (not sure what we should do about this)

This currently breaks the test environment. Normally zaken shouldn't be deleted outside of OAB, but this still happens so we need to make sure that this scenario is handled without breaking

Todo

Backend

• Fix helptext
• Fix api docs

Frontend

• Update types
• Dont crash if zaak is null