public function lock_message($config = array())
    {
        $config = new ObjectConfigJson($config);
        $config->append(array(
            'entity' => null
        ));

        if (!($config->entity instanceof ModelEntityInterface)) {
            throw new \UnexpectedValueException('$config->entity should be a ModelEntityInterface instance');
        }

        $entity = $config->entity;
        $message = '';

        if($entity->isLockable() && $entity->isLocked())
        {
            $user = $entity->getLocker();
            $date = $this->getObject('date', array('date' => $entity->locked_on));

            $message = $this->getObject('translator')->translate(
                'Locked by {name} {date}', array('name' => $user->getName(), 'date' => $date->humanize())
            );
        }

        return $message;
    }