Removing score from an existing test returns a server error

[sirQuail]

Removing the score from an existing graded test returns "Failed to edit test".

Steps to reproduce

• Edit a graded test and save.
• Example json to PUT:
  { "date": "2025-09-13", "type": "presentation", "result": "passed", "comments": "Free text" }

Implementation guidance

It seems to be a backend issue as Postman also returns a 500 error.
A possible solution is to pass an empty score when using PUT Update test.