useradmin mandatory email addr

Dear All,

Refer to the useradmin web interface (http://aaa.com/useradmin), the email address of a person is a mandatory field, is there anyway to modify so that it is not mandatyory field?

This is because I use a LDAP as readonly user datasource, if the LDAP user does not have email address entered in LDAP repository, in useradmin, I can't add/remove role because it will prompt that email address is missing during save.

Anybody can help? Thanks very much !

Regards,

Kelvin