How do I enable logging in XStream?

I am trying to load a manually transformed XML file using XStream. I no longer get an exception when unmarshalling it, but in the resulting objects the paths are null, which I don't expect it to be null.

Is there a way to enable debug logging in the XStream to help me identify the problem (JVM arguments or via my log config)? If not, suggestions on where to set breakpoints will be appreciated. Thank!