A customer reported receiving a 500 error in the frontend after activating the Joomla "Articles" module when accessing the link. Deactivating the module resolves the issue.

To reproduce the problem, I created a new module called "Articles." I selected no categories but enabled the "Show main articles" filter.

Expectation:
The module would be displayed, but only showing main articles.

Result: Error 500.

Reason:
If no category is selected, a 500 error appears in the frontend. Therefore, specifying/selecting a category is mandatory, even if the "Main articles" filter is intended to display only main articles.

Possible solution:
Make the "Categories" field mandatory. If no category is selected, a message should appear when saving the module indicating that a category selection is missing and the module cannot be saved.

This is a possible solution, but perhaps the Joomla community has a better suggestion.