Fix series dropdown not displaying "No options selected"

[Arnei]

In the metadata of the event details, if a series was already selected and then "No option selected" would be selected, it would still display the previously selected series. It would technically still work, it was just the display that was wrong. This fixes that.

Bildschirmaufzeichnung.vom.2026-01-09.12-26-55.webm

How to test this

Can be tested as usual.

[github-actions]

Use docker or podman to test this pull request locally.

Run test server using develop.opencast.org as backend:

podman run --rm -it -p 127.0.0.1:3000:3000 ghcr.io/opencast/opencast-admin-interface:pr-1500

Specify a different backend like stable.opencast.org:

podman run --rm -it -p 127.0.0.1:3000:3000 -e PROXY_TARGET=https://stable.opencast.org ghcr.io/opencast/opencast-admin-interface:pr-1500

It may take a few seconds for the interface to spin up.
It will then be available at http://127.0.0.1:3000.
For more options you can pass on to the proxy, take a look at the README.md.

[github-actions]

This pull request is deployed at test.admin-interface.opencast.org/1500/2026-01-09_11-28-19/ .
It might take a few minutes for it to become available.