Steps to reproduce the issue

1. Install Group choice activity (https://moodle.org/plugins/mod_choicegroup)

   cd $yoursiteroot/mod

   git clone git@github.com:ndunand/moodle-mod_choicegroup.git choicegroup

   cd choicegroup

   git checkout -b 2023061400 2023061400

1. Set 'Debug messages' = 'DEVELOPER' and 'Display debug messages' = Yes in Site administration > Development > Debugging and Save changes
2. Create a course with one group.
3. Add a Group choice activity to the course.
4. Remove the group.
5. Access the "Bulk edit activity completion", select the Group choice activity created in step #2 and click the Edit button.
6. Change some values and Save changes

The error shouldn't break the whole page.