--- loncom/homework/functionplotresponse.pm	2011/12/10 18:10:56	1.90
+++ loncom/homework/functionplotresponse.pm	2011/12/26 01:48:10	1.91
@@ -1,7 +1,7 @@
 # LearningOnline Network with CAPA
 # Functionplot responses
 #
-# $Id: functionplotresponse.pm,v 1.90 2011/12/10 18:10:56 www Exp $
+# $Id: functionplotresponse.pm,v 1.91 2011/12/26 01:48:10 www Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -1669,7 +1669,7 @@ sub functionplotrulecheck {
 #
 # Evaluate the value
 #
-   if ($value=~/\D/) {
+   if (($value=~/\D/) && ($value ne 'undef')) {
       $Apache::functionplotresponse::fpr_xmin=$xmin;
       $Apache::functionplotresponse::fpr_xmax=$xmax;
       $value=&Apache::run::run($value,$safeeval);