public function searchPickupPoints($postcode = null, $street_address = null, $country = null, $service_provider = null, $limit = 5)
    {
        if ( ($postcode == null && $street_address == null) || (trim($postcode) == '' && trim($street_address) == '') ) {
            return '[]';
        }

        $post_params = array(
            'postcode'          => (string) $postcode,
            'address'           => (string) $street_address,
            'country'           => (string) $country,
            'service_provider'  => (string) $service_provider,
            'limit'             => (int) $limit
        );

        return $this->doPost('/pickup-points/search', $post_params);
    }