docs: def _count(self, cmd, collation=None):
          """Internal count helper."""
          with self._socket_for_reads() as (sock_info, slave_ok):
              res = self._command(
                  sock_info, cmd, slave_ok,
                  allowable_errors=["ns missing"],
                  codec_options=self.__write_response_codec_options,
                  read_concern=self.read_concern,
                  collation=collation)
          if res.get("errmsg", "") == "ns missing":
              return 0
          return int(res["n"])