[Exim] dnsdb error

Running dnsdb and getting a failed result. If the lookup fails - the
filter rule fails. Is there any way of bypassing this?

lookup of "ns=162.23.67.in-addr.arpa" gave DEFER:

2003-12-20 06:45:52 1AXcIT-0005dn-7U Error in system filter: failed to
expand "X-Sender-Nameserver: ${sg{${lookup
dnsdb{ns=${sg{$sender_host_address}{\N([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3})\N}{\N$3.$2.$1.in-addr.arpa\N}}}}
${lookup
dnsdb{ns=${sg{$sender_host_address}{\N([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3}).([0-9]{1,3})\N}{\N$2.$1.in-addr.arpa\N}}}}}{\n}{
}}" in headers command: lookup of "ns=162.23.67.in-addr.arpa" gave DEFER: