I've found two small problems in the XIFF library.
The first one is in the XMPPConnection.getRegistrationFields_result, it looks like this method does not dispatch an event while it should. I think I fixed it. However, I'm not sure about this one.
The second one is in RegisterExtension.key. This returns a property of the myKeyNode propery, even though this could be null. If it is null this throws an error, I fixed this too.
The patch file is attached.
I've added another patch file here: http://www.igniterealtime.org/community/thread/35467.
Please consider granting me commit rights, I'm working on a rather large project and I might run into more problems that I can fix.