build: gradle task `publishNebulaPublicationToMavenLocal` always fails

[rursprung]

when building a new version of the plugin locally i use ./gradlew build publishToMavenLocal, however then it fails with this error:

> Task :publishNebulaPublicationToMavenLocal FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':publishNebulaPublicationToMavenLocal'.
> Failed to publish publication 'nebula' to repository 'mavenLocal'
   > Invalid publication 'nebula': groupId cannot be empty.

i have to exclude this task (i.e. run ./gradlew build publishToMavenLocal -x publishNebulaPublicationToMavenLocal) for the build to succeed.

i'm not familiar with nebula and what this task is doing, so i don't know what the appropriate fix would be. but it seems wrong that this step would fail?