docs: public static String getTopicID(final URI relativePath) {
          final String fragment = relativePath.getFragment();
          if (fragment != null) {
              final String id = fragment.lastIndexOf(SLASH) != -1
                                ? fragment.substring(0, fragment.lastIndexOf(SLASH))
                                : fragment;
              return id.isEmpty() ? null : id;
          }
          return null;
      }