Make it possible to deselect all categories.
Make it possible to deselect all categories.

This is a gotcha with HABTM checkboxes (i.e "topic[category_ids][]").
If all checkboxes are deselected, no category_ids will be submitted from the browser.

holderdeord/hdo-site,holderdeord/hdo-site,holderdeord/hdo-site,holderdeord/hdo-site