code: private EvaluationResult callHelper(URI type, URI id, URI issuer,
                                          URI category, int adType) {
          if (finder != null) {
              return finder.findAttribute(type, id, issuer, category,
                                          this, adType);
          } else {
              logger.warn(NO_FINDER_MSG);
  
              return new EvaluationResult(BagAttribute.createEmptyBag(type));
          }
      }
docs: Private helper that calls the finder if it's non-null, or else returns
  an empty bag