Index: src/java/org/sakaiproject/tool/assessment/ui/listener/evaluation/HistogramListener.java
===================================================================
--- src/java/org/sakaiproject/tool/assessment/ui/listener/evaluation/HistogramListener.java     (revision 54291)
+++ src/java/org/sakaiproject/tool/assessment/ui/listener/evaluation/HistogramListener.java     (working copy)
@@ -853,7 +853,16 @@
     int[] heights = calColumnHeight(numarray,responses);
     // int[] heights = calColumnHeight(numarray);
     for (i=0; i<bars.length; i++)
-      bars[i].setColumnHeight(Integer.toString(heights[i]));
+       {
+         try
+         {
+           bars[i].setColumnHeight(Integer.toString(heights[i]));
+         }
+         catch(NullPointerException npe)
+         {
+           log.warn("null column height " + npe);
+         }
+       }
     qbean.setHistogramBars(bars);
     qbean.setNumResponses(responses);
     if (responses > 0)