private void addServerInstance(List<ServerInstance> nodeList, ServerInstance serverInstance) {
            if (nodeList.contains(serverInstance)) {
                return;
            }
            nodeList.add(serverInstance);
        }
@author emeroad
@author netspider
@author minwoo.jung
@author HyunGil Jeong
web/src/main/java/com/navercorp/pinpoint/web/applicationmap/nodes/ServerGroupList.java