Is there any client side logging maintained? One thing I'm seeing is org.jboss.as.protocol.mgmt.ManagementRequest.responseBodyHandler lets any IOException propagate back to the Connection, which will just log it as an ERROR and carry on. This could result in the NPE.
Whether or not you have logging that demonstrates this is what's happening in your hudson failures, I need to fix the above; I should be able to get a patch done tonight; at least on a branch if not upstream.
If my theory is right though, the patch won't fix your test; it will just make the real problem more visible.