It seems that Groovy 3.0 was released (https://groovy-lang.org/releasenotes/groovy-3.0.html)

The Java Platform Module System requires that classes in distinct modules have distinct package names. Groovy has it’s own "modules" but these haven’t historically been structured according to the above requirement. For this reason, Groovy 2.x and 3.0 should be added to the classpath not module path when using JDK9+.

JDK requirements

Groovy 3.0 requires JDK9+ to build and JDK8 is the minimum version of the JRE that we support.

I bumped groovy version in tigase-projects-parent and tigase-http-api (and also made some adjustments to code).

As #ttsng-55 passes I would consider this fixed.