code: @Override
      public final Iterable<HeadDocument> findAll(
              final RootDocument rootDocument) {
          final Iterable<HeadDocument> headDocuments =
                  findAll(rootDocument.getFilename());
          if (headDocuments == null) {
              return null;
          }
          for (final HeadDocument headDocument : headDocuments) {
              final Head head = headDocument.getGedObject();
              head.setParent(rootDocument.getGedObject());
          }
          return headDocuments;
      }
docs: {@inheritDoc}