@Override
  public void removeSessionAttribute(String key) {
    if (key != null && !key.isEmpty()) {
      Map<String, Object> sessionAttributes = new HashMap<>(getSessionAttributes());
      sessionAttributes.remove(key);
      setSessionAttributes(sessionAttributes);
    }
  }
@param serviceName name of the service
@param componentName name of the component
@return the set of hosts for the provided service and component
ambari-server/src/main/java/org/apache/ambari/server/state/cluster/ClusterImpl.java