public function handleMetadataLoad(MetadataLoadEvent $event)
    {
        $metadata = $event->getMetadata();

        if (false === $metadata->getReflectionClass()->isSubclassOf(RobotBehavior::class)) {
            return;
        }

        $metadata->addFieldMapping(
            'noFollow',
            [
                'encoding' => 'system',
                'property' => 'noFollow',
            ]
        );

        $metadata->addFieldMapping(
            'noIndex',
            [
                'encoding' => 'system',
                'property' => 'noIndex',
            ]
        );
    }