See this old post why this is a good idea: https://dzone.com/articles/automatic-module-name-calling-all-java-library-maintainers

TLDR:
It costs nothing, has no compatibility issues and improves the usability of the library for JPMS enabled projects.
All that is needed is a single line in the MANIFEST.MF:

Automatic-Module-Name: org.jboss.marshalling
Automatic-Module-Name: org.jboss.marshalling.river
Automatic-Module-Name: org.jboss.marshalling.serial