As you can see in the config this is just a draft to check what's possble.
As the empty package is not supported I chose to define a //nopackage string as an alternative to the default values (for the cases there are "real" groovy files).

So a file must either start with one of those (taking package from the default list here).

//nopackage
File buildLog = new File( basedir, 'build.log' )
assert buildLog.exists()

or

package whatever
File buildLog = new File( basedir, 'build.log' )
assert buildLog.exists()

To automatically adding a licence, I would (re-)create the <file>config/maven-header-plain.txt</file> file, which is mentioned in the java configuration but does not exists and therefore is not applied.

I tested with some files in the PMD-plugin to ensure the configuration (file recognition, removing semicolons, adding licence) works

edit: Hmm the regEx seems to be wrong, all groovy files are effected, even those who have a licences, but maybe that is because the ASF licences not matched the given licence in the config. Have to check.

config/maven-header-plain.txt is taken from https://github.com/apache/maven-shared-resources/tree/master/src/main/resources/config
as maven-shared-resources is on plugin dependencies files are available on classpath

config/maven-header-plain.txt is taken from https://github.com/apache/maven-shared-resources/tree/master/src/main/resources/config as maven-shared-resources is on plugin dependencies files are available on classpath

Hm it's not applied. It just stays empty when I set this fileset :(