Auditor crashing on something

Got this error when the Signer Engine wanted audit the zone 88.168.192.in-addr.arpa

Aug 13 07:26:51 fou ods-auditor[3878]: Auditor starting on 88.168.192.in-addr.arpa
Aug 13 07:26:51 fou ods-auditor[3878]: SOA differs : from 2008104301 to 2008104303
Aug 13 07:26:51 fou ods-auditor[3878]: Auditing 88.168.192.in-addr.arpa zone : NSEC SIGNED
Aug 13 07:26:51 fou ods-auditor[3878]: Unexpected error auditing files (/home/rickard/opendnssec/tmp/88.168.192.in-addr.arpa.unsorted and /home/rickard/opendnssec/tmp/88.168.192.in-addr.arpa.finalized) : ERR undefined method `subdomain_of?' for nil:NilClass- moving on to next zone. Trace for debugging : /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:1043:in `out_of_zone' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:322:in `check_signature' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:760:in `load_signed_subdomain' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:166:in `check_zone' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:126:in `open' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:126:in `check_zone' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:125:in `open' /usr/local/lib/opendnssec/kasp_auditor/auditor.rb:125:in `check_zone' /usr/local/lib/opendnssec/kasp_auditor.rb:212:in `full_audit' /usr/local/lib/opendnssec/kasp_auditor.rb:166:in `run_with_syslog' /usr/local/lib/opendns

Perhaps something to do with this data in the signed zone(error from the signer):
\000\000\000\00288.168.192.in-addr.arpa. 604800 IN PTR oskar.rr.gunger.se.