Index: trunk/ppStack/src/ppStackLoop.c
===================================================================
--- trunk/ppStack/src/ppStackLoop.c	(revision 19486)
+++ trunk/ppStack/src/ppStackLoop.c	(revision 19505)
@@ -12,5 +12,5 @@
 #include "ppStack.h"
 
-//#define TESTING
+#define TESTING
 
 #define WCS_TOLERANCE 0.001             // Tolerance for WCS
@@ -529,4 +529,8 @@
         for (int i = 0; i < num; i++) {
             pmCell *inCell = cells->data[i]; // Input cell
+            if (!inCell) {
+                exptimes->data.F32[i] = 0.0;
+                continue;
+            }
             exptimes->data.F32[i] = psMetadataLookupF32(NULL, inCell->concepts, "CELL.EXPOSURE");
             psListAdd(cellList, PS_LIST_TAIL, inCell);