protected RegistrationConfigurator(IContainerRegistrar registrar = null)
        {
            Registrar = registrar ?? new NullContainerRegistrar();

            _consumers         = new RegistrationCache <IConsumerRegistration>();
            _sagas             = new RegistrationCache <ISagaRegistration>();
            _executeActivities = new RegistrationCache <IExecuteActivityRegistration>();
            _activities        = new RegistrationCache <IActivityRegistration>();
            _endpoints         = new RegistrationCache <IEndpointRegistration>();
        }