Steps to reproduce

1. Create a database activity
2. In the Activity completion section, select "Show activity as complete when conditions are met" in Completion tracking.
3. Remove all the rules (Require view, Require grade...).
4. Save changes

Expected behaviour

An error is displayed (something like "When you select automatic completion, you must also enable at least one requirement (below).").

Current behaviour

The database activity is saved (and no error is displayed).