Docker: Plugins Not Installed When Using ETHERPAD_PLUGINS Build Argument

[techware01]

Describe the bug
When building a new Docker container with preinstalled plugins using the ETHERPAD_PLUGINS build argument, the specified plugins are not installed. Despite providing the argument during the build, no plugins are present in the final container.

To Reproduce
Steps to reproduce the behavior:

1. Clone Repo
2. Checkout latest version v2.2.7
3. Run docker build --build-arg ETHERPAD_PLUGINS="ep_align ep_author_hover ep_comments_page" --tag test/etherpad .
4. Run newly build docker container docker run --publish 9001:9001 -e ADMIN_PASSWORD=admin test/etherpad
5. Open Etherpad admin page and see that no plugins where installed

Expected behavior
Plugins provided in the argument should be installed.

Server (please complete the following information):

• Etherpad version: 2.2.7
• OS: Arch Linux
• Docker Env

Additional context
When I add an echo statement in the Dockerfile to display the ETHERPAD_PLUGINS argument before the installation step, it shows up as empty. However, when I declare the ARG in the production stage beneath FROM build AS production, it works correctly. This behavior aligns with the information found in this Stack Overflow post.