docs: private void generateBackLinks(final Metadata m, final Element e) {
          final Element backLinksElements = new Element("backLinks", NS);
          for (final URL backLink : m.getBackLinks()) {
              addNotNullElement(backLinksElements, "backLink", backLink);
          }
          if (!backLinksElements.getChildren().isEmpty()) {
              e.addContent(backLinksElements);
          }
      }