zend_parse_parameters 's!' for NULL string ok?

The documentation claims: The following characters also have a meaning in the specifier string: ! - the parameter it follows can be of specified type or NULL (only applies to a, o, O, r, and z). If NULL value is passed by the user, the storage pointer will be set to NULL. Does the '!' character also work with strings (s)? It seems to work but I just want to make sure. Mike [1] http://www.zend.com/apidoc/zend.arguments.retrieval.php