Braintree\AddressGateway::_validateCustomerId PHP Method

    private function _validateCustomerId($id = null)
    {
        if (empty($id) || trim($id) == "") {
            throw new InvalidArgumentException('expected customer id to be set');
        }
        if (!preg_match('/^[0-9A-Za-z_-]+$/', $id)) {
            throw new InvalidArgumentException($id . ' is an invalid customer id.');
        }
    }