Github user afs commented on the issue:
https://github.com/apache/jena/pull/401
I ran:
/usr/lib/jvm/java-9-openjdk-amd64/bin/jdeps -cp 'lib/*'
lib/jena-arq-3.8.0-SNAPSHOT.jar
and the only split packages reported are for Xerces/xml-apis. Various
packages under javax.xml, org.w3c.dom and org.xml.sax split (clashing) with the
java runtime libraries.---
