How to debug openfire plugin?

I found a plugin online and I am trying to test it.

Built the plugin with openfire 3.9.3, deployed to my openfire server, everything seemed to be fine.

When I click on plugin’s admin setting page, I got a completely blank screen, even the openfire decorator didn’t show up.

How do I debug this kind of behavior? I’ve looked at error.log but nothing related to the plugin in trouble was shown.

-update:

After a pain in the a$$ manual debug session I figured out this line in the jsp is causing problem:

List multiparts = new ServletFileUpload(new DiskFileItemFactory()).parseRequest(request)

If I disable the line, the setting page shows up fine. This line is used for the setting page because the page allows users to upload stuff.

Any one knows how to fix it?

Thanks for your help.