private NodeConnectionState nodeState(String id) {
        NodeConnectionState state = this.nodeState.get(id);
        if (state == null)
            throw new IllegalStateException("No entry found for connection " + id);
        return state;
    }
Get the state of a given node.
@param id the connection to fetch the state for
clients/src/main/java/org/apache/kafka/clients/ClusterConnectionStates.java