Describe the bug

When creating a new programming exercise with an auxiliary repository, the download repository functionality does not work (the repository does not seem to be created by default by localCI)

To Reproduce

• 1 instructor

1. Create a new programming exercise
2. Edit the programming exercise, create an auxiliary repository
3. Try to download the auxiliary repository
4. See that you will receive an error message in the network tab but not an alert in the client
5. See that no auxiliary repository was created

Expected behavior

1. An alert should be displayed for the error in the network tab

(2. The download should work for localCI - maybe it would be possible to create / delete the auxiliary repository according to the changes in the UI?)

Screenshots

Which version of Artemis are you seeing the problem on?

7.1.0

What browsers are you seeing the problem on?

Chrome

Additional context

No response

Relevant log output

{
    "headers": {
        "normalizedNames": {},
        "lazyUpdate": null
    },
    "status": 500,
    "statusText": "Internal Server Error",
    "url": "http://localhost:9000/api/programming-exercises/153/export-instructor-auxiliary-repository/19",
    "ok": false,
    "name": "HttpErrorResponse",
    "message": "Http failure response for http://localhost:9000/api/programming-exercises/153/export-instructor-auxiliary-repository/19: 500 Internal Server Error",
    "error": {}
}