If you're seeing an error similar to:
null string many times in regex; marked by <-- HERE in m/\G(?:(?<=[\s,]))* <-- HERE \Z/ at /opt/local/lib/perl5/5.8.7/Text/Wrap.pm line 46.
This issue is popping up more and more on the users list and in irc. The short version is that newer versions of Text::Wrap (not associated with SpamAssassin) throw this warning for a regular expression that has been in use for years. It's been reported as a bug to the Text::Wrap authors already. More information can be found in SpamAssassin Bugzilla ticket 5056: