docs: def ReadClientStartupInfo(self, client_id, cursor=None):
      """Reads the latest client startup record for a single client."""
      query = (
          "SELECT startup_info, UNIX_TIMESTAMP(timestamp) "
          "FROM clients, client_startup_history "
          "WHERE clients.last_startup_timestamp=client_startup_history.timestamp "
          "AND clients.client_id=client_startup_history.client_id "
          "AND clients.client_id=%s")
      cursor.execute(query, [db_utils.ClientIDToInt(client_id)])
      row = cursor.fetchone()
      if row is None:
        return None
  
      startup_info, timestamp = row
      res = rdf_client.StartupInfo.FromSerializedString(startup_info)
      res.timestamp = mysql_utils.TimestampToRDFDatetime(timestamp)
      return res