Saving all quick grading changes for no users results in coding error: moodle_database::get_in_or_equal() does not accept empty arrays

In a course with no students, clicking "Save all quick grading changes" for an assignment results in a coding error:

"Coding error detected, it must be fixed by a programmer: moodle_database::get_in_or_equal() does not accept empty arrays"

Steps to reproduce:

1. Create a course but do not enroll any students in the course.
2. Create an assignment.
3. Open assignment.
4. Click View/Grade All Submissions.
5. Make sure quick grading is on and note that "Save all quick grading changes" button displays.
6. Click "Save all quick grading changes" button.

Expected result: Either the save changes button shouldn't display at all, or if it does and someone clicks it, a friendly message should be received to the effect of "There are no submissions to save."

Actual result: Coding error.