code: @Reference(service = Controller.class,
                 cardinality = ReferenceCardinality.OPTIONAL,
                 policy = ReferencePolicy.DYNAMIC,
                 policyOption = ReferencePolicyOption.GREEDY)
      protected void setController(ServiceReference<Controller> ref) {
          controllerRef.setReference(ref);
      }
docs: Declarative Services method for setting the controller
  
  @param ref reference to the service