Sometimes the frontend sends undefined as assignmentId / courseId
Example
mleeuwis 145.94.212.225 [04/Sep/2020:17:01:49 +0000] "GET /api/courses/undefined/enrolledassignments HTTP/1.1" 400 38
mbloembergen 80.112.147.98 [05/Sep/2020:12:58:50 +0000] "GET /api/assignments/undefined/submissions?groupId=13021 HTTP/1.1" 400 38
mbloembergen 80.112.147.98 [05/Sep/2020:12:58:58 +0000] "GET /api/assignments/undefined/group HTTP/1.1" 400 38