Crashes if you accidentally select assignment with no points

Canvas allows assignments to display grades in different manners:

I accidentally selected an assignment with Complete/Incomplete set on it, and the script just crashed:

Traceback (most recent call last):
  File "./analyze_grades.py", line 147, in <module>
    assess_course(course_selection)
  File "./analyze_grades.py", line 138, in assess_course
    assess_assignments(course, major_partitions, answer != '' and answer[0].upper() == 'Y')
  File "./analyze_grades.py", line 106, in assess_assignments
    print_statistics(oat_assignment, major_partitions)
  File "./analyze_grades.py", line 74, in print_statistics
    print_statistics_for_some_majors(assignment, computing_majors, major_partitions)
  File "./analyze_grades.py", line 59, in print_statistics_for_some_majors
    scores: List[float] = [assignment.get_score(student) for student in student_subset
  File "./analyze_grades.py", line 60, in <listcomp>
    if assignment.get_score(student) is not None]
  File "/home/fac/cabohn/abet-oat/api/canvas_classes.py", line 523, in get_score
    return float(submission.grade) if submission.grade is not None else None
ValueError: could not convert string to float: 'complete'

The script probably should handle that a bit more gracefully.

And I do not have any assignments to test it, but suspect if one is set to something other than Points (such as Percentage) it would probably not work as expected--though it might not crash in that case.

Another edge case is probably if the total points is set to 0 - does it divide by 0 on line 63?