public function onMoveContent(EventInterface $event)
    {
        $translator = $this->getTranslator();
        $mapper = $this->getLayoutMapper();
        if (is_null($event->getParam('tid'))) {
            throw new InvalidArgumentException(
                $translator->translate(
                    "Unknown transaction identifier. Missing event param 'tid'."
                )
            );
        }
        if (is_null($event->getParam('content'))) {
            throw new InvalidArgumentException(sprintf(
                $translator->translate(
                    "Missing event param '%s'."
                ),
                'content'
            ));
        }
        $mapper->unregisterContent(
            $event->getParam('content'),
            false,
            $event->getParam('tid')
        );
    }