--- trunk/pg/lib/Value/AnswerChecker.pm	2005/08/12 17:09:42	3487
+++ trunk/pg/lib/Value/AnswerChecker.pm	2005/08/12 17:40:07	3488
@@ -480,6 +480,7 @@
 #
 sub protectHTML {
     my $string = shift;
+    return unless defined($string);
     return $string if eval ('$main::displayMode') eq 'TeX';
     $string =~ s/&/\&/g;
     $string =~ s/</\&lt;/g;