[syslog-ng] patterndb can't match empty log strings

All, Sometimes an empty log message is emitted, but I can't match it using pdbtool. I've tried patterns such as: <pattern>@ANYSTRING@</pattern> <pattern></pattern> <pattern> </pattern> Nothing works. Other log messages from the same application are definitely being matched by the @ANYSTRING@, so I know my rule is working. So is there a way to specify an empty log string? Do I have to use a regex instead? Thanks, -Kurt