Request users from Canvas instead of courses

src/canvaslms/cli/submissions.nw

@@ -753,13 +753,29 @@ def resolve_grader(submission):
     return "autograded"
 
   try:
-    return submission.assignment.course.get_user(submission.grader_id)
+    <<resolve the grader's user ID from Canvas>>
   except canvasapi.exceptions.ResourceDoesNotExist:
     canvaslms.cli.warn(f"unknown grader {submission.grader_id} "
                        f"for submission {submission}.")
     return f"unknown grader {submission.grader_id}"
 @
 
+The only option we have as the code is written currently, is to try to get the 
+user from the course ([[course.get_user]]).
+But we should really get the user from a Canvas object, [[canvas.get_user]].
+If using [[get_user(...)]] on a course object, then the user must exist in the 
+course.
+However, that's not necessarily true.
+So we should get it from a [[Canvas]] object, that is, from the system rather 
+than just the course.
+But as mentioned, right now we can only do it through the course.
+This isn't a problem as long as none of the teachers or teaching assistants are 
+removed.
+<<resolve the grader's user ID from Canvas>>=
+return submission.assignment.course.get_user(submission.grader_id)
+@
+
+
 \subsection{Rubric data}
 
 <<add rubric assessment to output>>=