code: @Override
      public final HeadDocument findByFileAndString(
              final String filename, final String string) {
          final Query searchQuery = new Query(Criteria.where("string").is(string)
                  .and("filename").is(filename));
          final HeadDocument headDocument =
                  mongoTemplate.findOne(searchQuery, HeadDocumentMongo.class);
          if (headDocument == null) {
              return null;
          }
          final Head head =
                  (Head) toObjConverter.createGedObject(null, headDocument);
          headDocument.setGedObject(head);
          return headDocument;
      }
docs: {@inheritDoc}