public void addServer(Server server) {
        if (server != null) {
            try {
                serverStatsCache.get(server);
            } catch (ExecutionException e) {
                ServerStats stats = createServerStats(server);
                serverStatsCache.asMap().putIfAbsent(server, stats);
            }
        }
    }
The caller o this class is tasked to call this method every so often if
the servers participating in the LoadBalancer changes
@param servers
ribbon-loadbalancer/src/main/java/com/netflix/loadbalancer/LoadBalancerStats.java