code: public Optional<String> getMessage(final String code) {
          for(final ResourceBundle bundle : messageBundles) {
              final List<String> keys = messageBundleKeys.get(bundle);
              if(keys.contains(code)) {
                  try {
                      return Optional.of(bundle.getString(code));
                  } catch(MissingResourceException e) {
                      return Optional.empty();
                  }
              }
          }
          
          return Optional.empty();
      }
docs: {@inheritDoc}