[exim] About ldap lookup without non-exit attribute

Hi all


Now I debug exim quota ,the field of quota is quotaBytes,but many users
have no the attribute(quotaBytes),for theses users i want to give a
default quota(600),how do I do for this ldap lookup?

Please tell me if you know.Thanks.

quota = ${lookup ldap {user="cn=servers,dc=xxxx1,dc=com" pass=passdddd
ldap:///cn=$local_part,cn=users,dc=xxxx1,dc=com?quotaBytes}{$value}{600}}


The above line is my config,but it don't work !!!!!