What causes a "Cannot register a null resource" error in ICEfaces?

Question

Java EE 5, JSF 1.2 with Facelets, ICEfaces 1.8.2

What can cause a "Cannot register a null resource" error in ICEfaces, using an ice:outputResource tag? From the ICEfaces source code, it looks like it's when the resource is null (duh), but I'm positive that it isn't. Are there any other possible causes?

Answer 1

Oh, I got it. The Resource was an anonymous class, and one of the inherited methods I implemented in it (specifically, com.icesoft.faces.context.Resource.calculateDigest()) sometimes caused a NullPointerException that was nowhere to be seen in the stack trace.

I'm often frustrated with Java technologies' error messages; my productivity could probably be increased by 25% by having detailed, helpful error messages (it's a feature!).