Retrieve the data associated with a named subscription

        Returns None if there is no data associated with `name`

        If root is not None, then only return the subscription
        data that matches both root and name.  When used in this way,
        remove processing impacts both the unscoped and scoped stores
        for the subscription data.

async def get_subscription(self, name, root):
        """ Retrieve the data associated with a named subscription

        Returns None if there is no data associated with `name`

        If root is not None, then only return the subscription
        data that matches both root and name.  When used in this way,
        remove processing impacts both the unscoped and scoped stores
        for the subscription data.
        """
        self._check_receive_loop()
        self._ensure_subscription_queue_exists(name, root)
        res = await self.sub_by_root[root][name].get()
        self._check_error(res)
        return res