docs: public List<ModelServiceInstance> getUPModelInstances(String serviceName){
          ModelService service = getModelService(serviceName);
  
          List<ModelServiceInstance> list = null;
          if(service != null && service.getServiceInstances().size() > 0){
  
              for(ModelServiceInstance instance : new ArrayList<ModelServiceInstance>(service.getServiceInstances())){
                  if(instance.getStatus().equals(OperationalStatus.UP)){
                      if(list == null){
                          list = new ArrayList<ModelServiceInstance>();
                      }
                      list.add(instance);
                  }
              }
  
          }
  
          if(list == null){
              return Collections.emptyList();
          }else{
              return list;
          }
      }