If you use newer RFC2307Bis schema for managing POSIX group members by "member" atribute, you probably found out that you cannot use group without at least one member because the class "groupOfNames" requires it. The right way to correct this behaviour is to use the "groupOfEntries" class specified by this draft.
ldapadd -D cn=admin,cn=config -W -H <LDAP_server_url> -f /path/to/groupofentries.ldif