docs: def AddHashEntry(self, hash_entry, timestamp):
      """Registers hash entry at a given timestamp."""
  
      if timestamp in self._hash_entries:
        message = ("Duplicated hash entry write for path '%s' of type '%s' at "
                   "timestamp '%s'. Old: %s. New: %s.")
        message %= ("/".join(self._components), self._path_type, timestamp,
                    self._hash_entries[timestamp], hash_entry)
        raise db.Error(message)
  
      if timestamp not in self._path_infos:
        path_info = rdf_objects.PathInfo(
            path_type=self._path_type,
            components=self._components,
            timestamp=timestamp,
            hash_entry=hash_entry)
        self.AddPathInfo(path_info)
      else:
        self._path_infos[timestamp].hash_entry = hash_entry