code: @Override
      public Collection<String> findSurnameInitialLetters(
              final FinderObject owner) {
          logger.info("Starting findSurnameInitialLetters");
          final Set<String> matches = new TreeSet<>();
          if (owner instanceof Root) {
              final Root root = (Root) owner;
              final RootDocumentMongo rootDocument =
                      (RootDocumentMongo) toDocConverter.createGedDocument(root);
              final Iterable<PersonDocument> personDocuments =
                      repositoryManager.getPersonDocumentRepository().
                          findAll(rootDocument);
              for (final PersonDocument personDocument : personDocuments) {
                  final String firstLetter = personDocument.getSurname()
                          .substring(0, 1);
                  matches.add(firstLetter);
              }
          }
          logger.info("Ending findSurnameInitialLetters");
          return matches;
      }
docs: {@inheritDoc}