Mixing Kotlin and Java in a single module of a multi-module Maven or Gradle project

Hi,

does anyone have a multi module Maven or Gradle project in production? Basically I'm considering moving SirixDB to Kotlin and to write new classes in Kotlin.

However, I'm not sure. I've used Java from Kotlin but not the other way around. So, would you recommend adding Kotlin to the core module for instance or are there any pitfalls? I think Kotlin is just like a modern Java and I'm a bit resistent to write Java code in my spare time, now that I worked a bit with Kotlin ;-)

Kind regards
Johannes