code: @Override
      public R visitUnknown(AnnotationValue av, P p) {
          throw new UnknownAnnotationValueException(av, p);
      }
docs: {@inheritDoc}
  
  @implSpec The default implementation of this method in {@code
  AbstractAnnotationValueVisitor6} will always throw {@code
  new UnknownAnnotationValueException(av, p)}.  This behavior is not
  required of a subclass.
  
  @param av {@inheritDoc}
  @param p  {@inheritDoc}