public function determinePostalType($postalcode)
    {
        $postalcode = str_replace(' ', '', $postalcode);

        if (strlen($postalcode) == 6) {
            return ['nl_sixpp' => $postalcode];
        }

        if (strlen($postalcode) == 4) {
            return ['nl_fourpp' => $postalcode];
        }

        throw new \Exception('No valid postalcode was found (nl_sixpp or nl_fourpp)');
    }