It looks like the Next and Save and show next button does not work.

Environment
Moodle - 3.9.2+ (Build: 20201030)
mod_checklist - 2020012900

Replication
1. Create a course and enrol 3 students.
2. Turn editing on.
3. Add a Checklist activity and set Settings / Updates by = Student and teacher.
4. Click Save and display button.
5. In the Edit checklist tab, type: "my item 1" and click "Add button".
6. type another one, type: "my item 2" and click "Add button".
7. type another one, type: "my item 3" and click "Add button".
8. Click on the "View progress" tab.
9. Click on the magnifying icon next to the student's name.
10. The Checklist for "Student" page will be displayed. It will show the three items, plus the "Save", "Save and show next" and the "Next" buttons.
11. Click either the "Save and show next" or the "Next" button.

Observed:
A message is displayed "Warning: Invalid argument supplied for foreach() in [MOODLE]/mod/checklist/locallib.php on line 2654"
and the "View progress" gets refreshed".

Issue: The next buttons don't work and does not display the next student record.