code: public static Optional<AnnotationSpec> generatedAnnotationSpec(
        Elements elements, SourceVersion sourceVersion, Class<?> processorClass) {
      return generatedAnnotationSpecBuilder(elements, sourceVersion, processorClass)
          .map(AnnotationSpec.Builder::build);
    }
docs: Returns {@code @Generated("processorClass"} 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.