How can I debug a JSP?

Question

I'm trying to edit a JSP for a project and I'm getting a NullPointerException somewhere in the JSP when it's requested from my server.

My web server (JBoss) is reporting the exception, but it's giving me a bogus line number. It's reporting that the exception happened on line 702, but my JSP is only 146 lines long, so I'm unable to identify which line is choking.

What are some good techniques to debug errors in JSPs? I'm using IntelliJ 9 Ultimate as my IDE.

Thanks