<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _aggregate_one_result( self, sock_info, slave_ok, cmd, collation=None, session=None):
 """Internal helper to run an aggregate that returns a single result."""

        result = self._command(
            sock_info,
            cmd,
            slave_ok,
            codec_options=self.__write_response_codec_options,
            read_concern=self.read_concern,
            collation=collation,
            session=session)
        batch = result['cursor']['firstBatch']
        return batch[0] if batch else None