PDF previews don't work in docker container


I deployed a 10.14 owncloud server container and enabled the PDF provider via environment variables.
Previews were still not generated, because ImageMagick depends on ghostscript when trying to work with pdf files.

In the github repository “owncloud-docker/php” I found a pullrequest that added a command to the Dockerfile, that explicitly uninstalls ghostscript.

After manually installing ghostscript via “apt-get install ghostscript” in the container, owncloud was able to generate previews for pdf files.
Is it a bug or a feature?
Is there a place to document this?