Index: chart.module
===================================================================
--- chart.module	(revision 1094)
+++ chart.module	(working copy)
@@ -636,6 +636,9 @@
       }
       // Generate regular labels
       if (count($regular)){
+        if (!isset($data['chxl'])) {
+          $data['chxl'] = '';
+        }
         foreach($regular AS $axis => $indices){
           if (count($indices)){
             foreach($indices AS $i => $labels){
@@ -658,8 +661,11 @@
       }
       // Generate positions
       if (count($positions)){
+        if (!isset($data['chxp'])) {
+          $data['chxp'] = '';
+        }
         foreach($positions AS $i => $position){
-          if ($position['set'] == TRUE){
+          if (isset($position['set']) && $position['set'] == TRUE){
             $data['chxp'] .= $i . ',' . implode(',', $position['data']) .  '|';
           }
         }