code: public Set<String> getIdsPerName(final String surname, final String name) {
          if (surname == null || name == null) {
              return Collections.emptySet();
          }
          final Map<String, SortedSet<String>> namesPerSurname =
                  getNamesPerSurnameMap(surname);
          if (!namesPerSurname.containsKey(name)) {
              return Collections.emptySet();
          }
          return Collections.unmodifiableSet(namesPerSurname.get(name));
      }
docs: Get the set of IDs for the given surname and full name.
  
  @param surname the surname to search
  @param name the full name in index form
  @return the set of IDs