Construct a KeyRange protobuf.

        :rtype: :class:`~google.cloud.spanner_v1.proto.keys_pb2.KeyRange`
        :returns: protobuf corresponding to this instance.

def _to_pb(self):
        """Construct a KeyRange protobuf.

        :rtype: :class:`~google.cloud.spanner_v1.proto.keys_pb2.KeyRange`
        :returns: protobuf corresponding to this instance.
        """
        kwargs = {}

        if self.start_open is not None:
            kwargs["start_open"] = _make_list_value_pb(self.start_open)

        if self.start_closed is not None:
            kwargs["start_closed"] = _make_list_value_pb(self.start_closed)

        if self.end_open is not None:
            kwargs["end_open"] = _make_list_value_pb(self.end_open)

        if self.end_closed is not None:
            kwargs["end_closed"] = _make_list_value_pb(self.end_closed)

        return KeyRangePB(**kwargs)