Create username from "multi word" FirstName

I would like to choose Firstname as a username. Sometime people have 2 words in their FirstName. It looks like for multi word FirstName, all will be used as a username with spaces allowed. Isn't the following function not allowing that?

function _user_import_sanitise_username(&$username) {
// username cannot contain multiple spaces in a row
$username = preg_replace('/[ ]+/', ' ', $username);
....

}