--- /usr/share/perl5/Mail/SpamAssassin/Util.pm.orig     2014-08-22 00:08:39.185602751 +0200
+++ /usr/share/perl5/Mail/SpamAssassin/Util.pm  2014-08-22 00:09:18.330883723 +0200
@@ -285,7 +285,7 @@
   my $r = ref $_[0];
   if (!$r) {
     no re 'taint';  # override a  "use re 'taint'"  from outer scope
-    return if !defined $_[0];
+    return undef if !defined $_[0];
     local($1); # avoid Perl taint bug: tainted global $1 propagates taintedness
     $_[0] =~ /^(.*)\z/s;
     return $1;