Index: trunk/ippTasks/stack.pro
===================================================================
--- trunk/ippTasks/stack.pro	(revision 12369)
+++ trunk/ippTasks/stack.pro	(revision 12370)
@@ -141,5 +141,5 @@
 
     ## generate output log based on filerule
-    if ($WORKDIR == NULL)
+    if ("$WORKDIR" == "NULL")
       $outroot = `pwd`
     else
@@ -153,5 +153,5 @@
 
     $run = stack_skycell.pl --stack_id $STACK_ID $ARGS
-    if ($WORKDIR != NULL)
+    if ("$WORKDIR" != "NULL")
       $run = $run --workdir $outroot
     end