code: @Override
      public final HeadDocument findByRootAndString(
              final RootDocument rootDocument, final String string) {
          final HeadDocument headDocument =
                  findByFileAndString(rootDocument.getFilename(), string);
          if (headDocument == null) {
              return null;
          }
          final Head head = headDocument.getGedObject();
          head.setParent(rootDocument.getGedObject());
          return headDocument;
      }
docs: {@inheritDoc}