When I provide the fileset by picking every file in JAVA_HOME:

        Path jreOrJdk = Paths.get(CONFIG_INSTANCE.getOtherJre());
        fileSet = new RelativeFileSet(
                jreOrJdk.toFile(), Files.walk(jreOrJdk)
                .map(path -> path.toFile().getAbsoluteFile())
                .filter(File::isFile)
                .collect(Collectors.toSet())
        );

        additionalParams.put(BundleParams.PARAM_RUNTIME, fileSet);

Then I get the following ConfigException:

com.oracle.tools.packager.ConfigException: Java Runtime does not include [Contents/Home/jre/lib/[^/]+/libjvm.dylib, Contents/Home/jre/lib/rt.jar]