docs: protected void onServiceInstanceUnavailable(ServiceInstance instance){
          if(instance == null){
              return ;
          }
          String serviceName = instance.getServiceName();
          synchronized(notificationHandlers){
              if(notificationHandlers.containsKey(serviceName)){
                  for(NotificationHandler h : notificationHandlers.get(serviceName)){
                      h.serviceInstanceUnavailable(instance);
                  }
              }
          }
      }