[otrs] Cron Job Error

We receive the following error occasionally from the OTRS cron job: Use of uninitialized value in pattern match (m//) at /opt/otrs/Kernel/System/EmailParser.pm line 270. As far as we're aware, all mail is making it into the system and becoming tickets. We do not notice any tickets that are incomplete or empty. Everything appears to be fine other than receiving the message above. What is the error telling me, and how do I fix it? We are on OTRS version 2.2.5 with plans to upgrade to 2.26 in the near future.