public static function emptyValues($obj)
    {
        if (is_array($obj)) {
            $values = $obj;
        } elseif ($obj instanceof StripeObject) {
            $values = $obj->_values;
        } else {
            throw new \InvalidArgumentException(
                "empty_values got got unexpected object type: " . get_class($obj)
            );
        }
        $update = array_fill_keys(array_keys($values), "");
        return $update;
    }