Everything went swimmingly (except a minor error message because no logger
had been set) until the last page of my document.

      java.lang.NullPointerException
	at
org.apache.fop.apps.StreamRenderer.render(StreamRenderer.java:205)

At this point the StreamRenderer tries to log the
total page count. I guess there hasn't been a logger
set for the stream renderer. A quick glance into
com.icl.saxon.fop.FOPEmitter seems to confirm this,
an explicite StreamRenderer is createt there (as a
workaround for a FOP 0.20.1 deficency), and no logger
is set.

Because you have the source, you can fix that yourself,
deleting the statement mentioned above should be sufficient.