@Override
    public Server choose(Object key) {
        if (roundRobinRule != null) {
            return roundRobinRule.choose(key);
        } else {
            throw new IllegalArgumentException(
                    "This class has not been initialized with the RoundRobinRule class");
        }
    }
This class essentially contains the RoundRobinRule class defined in the
loadbalancer package

@author stonse
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/ClientConfigEnabledRoundRobinRule.java