"Replacing" an attribute's value with "nothing"

["Mudry, Robert (N-aerotek)" <robert.mudry@lmco.com>]

Is there a way I can set an attribute in my schema to allow me to "replace"
its value with ""? (That's nothing) Most of our code was designed for the
Netscape Directory Server, which allows replace operations of "". But
OpenLDAP has been complaining:

Return code: 21 Message: LDAP_INVALID_SYNTAX :Some part of the request
contained
 an invalid syntax. It could be a search
with an invalid filter or a request to modify the schema and the given
schema has a bad syntax.
MessageID: 57   DN

That's a Perl LDAP error message for: $mesg = $ldap->modify( $userdn,
replace => {'mail' => "" });

-Robert