code: public static Optional<AnnotationSpec> generatedAnnotationSpec(
        Elements elements, SourceVersion sourceVersion, Class<?> processorClass, String comments) {
      return generatedAnnotationSpecBuilder(elements, sourceVersion, processorClass)
          .map(annotation -> annotation.addMember("comments", "$S", comments).build());
    }
docs: Returns {@code @Generated(value = "processorClass", comments = "comments"} for the target
  {@code SourceVersion}.
  
  <p>Returns {@code javax.annotation.processing.Generated} for JDK 9 and newer, {@code
  javax.annotation.Generated} for earlier releases, and Optional#empty()} if the annotation is
  not available.