pt-deadlock-logger error: Use of uninitialized value $ts in pattern match (m//)

A customer has reported a case where the deadlock information causes:

Use of uninitialized value $ts in pattern match (m//) at /usr/bin/pt-deadlock-logger line 4143.

The lines around 4143:
4141 # Extract some miscellaneous data from the deadlock.
4142 my ( $ts ) = $dl_text =~ m/^$s$/m;
4143 my ( $year, $mon, $day, $hour, $min, $sec ) = $ts =~ m/^((?:\d\d)?\d\d)-?(\d\d)-?(\d\d) +(\d+):(\d+):(\d+)$/;
4144 if ( length($year) == 2 ) {
4145 $year += 2000;
4146 }
4147 $ts = sprintf('%02d-%02d-%02dT%02d:%02d:%02d', $year, $mon, $day, $hour, $min, $sec);
4148 my ( $victim ) = $dl_text =~ m/^\*\*\* WE ROLL BACK TRANSACTION \((\d+)\)$/m;
4149 $victim ||= 0;