Got the new Spring Data aggregation APIs working.  Still more work to do, however.
Merge remote-tracking branch 'origin/master'
Fleshed out more of the match statement.
Got the entire query in terms of Spring Data now.
Now match on the enrolled classes.
Ran into a blocker with the new aggregation APIs so I had to disable the test.  I opened up a bug and will hope for a fix.  In the meantime, we can use the older APIs.