For the 11.x branch, I'm observing another NPE for line 1519 in "getHighestSubmittedAssessmentGrading":

ag.setAssessmentGradingAttachmentList(attachments);

The 'ag' variable is null for the following scenario:

1. On a blank Lessons page, add a published quiz (Add Content -> Link to a test or quiz).
2. Click the "Edit" button that corresponds to the quiz on the Lessons page
3. In the "Edit Item" dialog, check "Require that the student submit this assessment." and click "Update Item".

An NPE should be logged in catalina.out.

Moving ag.setAssessmentGradingAttachmentList(attachments) up into the "if (ag != null)" conditional seems to resolve this problem.