Annotating fields in classes extended for a custom plugin

I’m currently working on some custom Gradle (v4.2.1) plugin code and, while all the code builds and tests perfectly fine, I’m getting a bunch of annotation warnings from the validateTaskProperties task. The warnings are referencing fields in classes that my plugin task code extends, not in the plugin code itself. Since the source code resides in delivered, built artifacts that I’m using I’m not sure how to resolve the warnings at the source code level without building my own version of the artifacts with the fields modified with the appropriate annotations. Is there any workaround for this?