A lot of HTTP/500 won't have anything more in Java.
But I would try the purepath route, as Chad said: on the top right of your page , click the Purepath icon,
When you see the Errors tab in the Purepath, see if there are other nested exceptions. Beware that you might have other exceptions not related to the 500 error though:
Sometimes you get more details on the Error tab of the PurePaths because the HttpServletResponse.setStatus() call is made is set based on an earlier exception, but other times, the code is simply setting the status based on some logic. In those cases, I don't believe there is much else you can get other than looking at the Code tab to see if you can determine what might have caused it, or checking logs for clues.