Illegal reflective access by org.grails.testing.runtime.support.ActionSettingMethodHandler

[monetschemist]

Running some unit tests today after some substantial changes in a project I'm developing and I received this message:

HomeControllerSpec > test index action FAILED
    java.lang.NullPointerException at HomeControllerSpec.groovy:10
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.grails.testing.runtime.support.ActionSettingMethodHandler (file:/home/clh/.gradle/caches/modules-2/files-2.1/org.grails/grails-web-testing-support/3.1.0/2858bd4f312668ac207e4fcebdf269b34f4737da/grails-web-testing-support-3.1.0.jar) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of org.grails.testing.runtime.support.ActionSettingMethodHandler
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

I note the Please consider reporting this to the maintainers but I'm not sure who they might be. Does anyone have any suggestions?

The class ActionSettingMethodHandler is easy to find in the source tree here but it seems the last change was six years ago.