JarModuleFinder.findModule() processes the Class-Path manifest, and processes the values as file paths. http://docs.oracle.com/javase/8/docs/technotes/guides/jar/jar.html says that the values are relative URLs, and some tools (e.g. Maven's SureFire/FailSafe plugins) create jars with absolute file: URLs.

It would be nice to support file: URLs there (relative or absolute), but non-file URLs are probably not wanted.