quarkus: Adding Groovy plugin to Gradle project fails quarkusDev

When adding the Groovy plugin like:

plugins {
    id "java"
    id "groovy"
    id "io.quarkus"
}

then quarkusDev fails with:

❯ ./gradlew clean quarkusDev

> Task :compileJava
Note: Some input files use unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

> Task :quarkusDev FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Some problems were found with the configuration of task ':quarkusDev' (type 'QuarkusDev').
> Directory '/Users/marceloverdijk/workspace/demo-backend-quarkus/build/classes/groovy/main' specified for property 'workingDir' does not exist.
> Directory '/Users/marceloverdijk/workspace/demo-backend-quarkus/src/main/groovy' specified for property 'sourceDir' does not exist.

It seems the src/main/groovy folder is expected.

I’m only adding Groovy to run Spock tests from /src/test/groovy.

When creating an empty src/main/groovy folder it keeps complaining about build/classes/groovy/main.