docs: public List<ModelServiceInstance> getModelInstancesByMetadataKey(String keyName){
          ModelMetadataKey key = getModelMetadataKey(keyName);
          if(key == null || key.getServiceInstances().isEmpty()){
              return Collections.<ModelServiceInstance>emptyList();
          }else{
              return new ArrayList<ModelServiceInstance>(key.getServiceInstances());
          }
      }