docs: @Reference(policy = ReferencePolicy.DYNAMIC, cardinality = ReferenceCardinality.MULTIPLE, target = "(config.displayId=*)")
      protected Map<String, Object> setUserRegistry(ServiceReference<UserRegistryService> ref) {
          adjustUserRegistryServiceRef(ref);
  
          // determine a new user registry service
          userRegistryService.set(null);
          return getServiceProperties();
      }