Full Java module descriptors (module-info.class) are a hard requirement for building custom Java Runtimes with Jlink.

It looks like the build must remain pre Java modules (Java 6? I suppose that's related to the lowest common denominator: Android), however given that the build is Gradle based there's the https://plugins.gradle.org/plugin/org.beryx.jar plugin that can be applied to keep the build in its current Java version while at the same time providing a full module descriptor. Caveat: the generated JAR will become a multi-release JAR.

If there's any interest I'll gladly provide a PR and help with maintenance.