public function createEvent(
        $event,
        $entityType,
        $entityId,
        $targetEntityType=null,
        $targetEntityId=null,
        array $properties=null,
        $eventTime=null
    ) {
        if (!isset($eventTime)) {
            $eventTime = new \DateTime();
        } elseif (!($eventTime instanceof \DateTime)) {
            $eventTime = new \DateTime($eventTime);
        }
        $eventTime = $eventTime->format(\DateTime::ISO8601);

        $data = [
            'event' => $event,
            'entityType' => $entityType,
            'entityId' => $entityId,
            'eventTime' => $eventTime,
        ];

        if (isset($targetEntityType)) {
            $data['targetEntityType'] = $targetEntityType;
        }

        if (isset($targetEntityId)) {
            $data['targetEntityId'] = $targetEntityId;
        }

        if (isset($properties)) {
            $data['properties'] = $properties;
        }

        $json = $this->jsonEncode($data);

        $this->export($json);
    }