def METHOD_NAME(self, client: ClientProxy) -> None:
    """Unregister Flower ClientProxy instance.
    This method is idempotent.
    Parameters
    ----------
    client : flwr.server.client_proxy.ClientProxy
    """
    if client.cid in self.nodes:
        node_id, ins_scheduler = self.nodes[client.cid]
        del self.nodes[client.cid]
        ins_scheduler.stop()
        # Unregister node_id in with State
        state: State = self.state_factory.state()
        state.unregister_node(node_id=node_id)
        with self._cv:
            self._cv.notify_all()