private function checkTitle(&$title)
    {
        if ( ! is_string($title)) {
            $type = gettype($title);

            throw new InvalidArgumentException("The title must be a string value, [$type] is given.");
        }

        $title = trim($title);

        if (empty($title)) {
            throw new InvalidArgumentException('The title is required and must not be empty.');
        }
    }