public static function getUserName(User $user, $defaultToLabel = false)
    {
        $firstName = self::getUserStringProp($user, GenerisRdf::PROPERTY_USER_FIRSTNAME);
        $lastName = self::getUserStringProp($user, GenerisRdf::PROPERTY_USER_LASTNAME);
        
        $userName = trim($firstName . ' ' . $lastName);
        
        if (empty($userName) && $defaultToLabel) {
            $userName = self::getUserLabel($user);
        }

        return $userName;
    }