throw multiples(true);
        }
        return this;
      }
    }

    @IgnoreJRERequirement // see enclosing class (whose annotation Animal Sniffer ignores here...)
    Optional<Object> getOptional() {
      if (extras.isEmpty()) {
        return Optional.ofNullable(element);
      } else {
        throw multiples(false);
      }
    }