Index: trunk/ppSub/src/ppSubReadout.c
===================================================================
--- trunk/ppSub/src/ppSubReadout.c	(revision 20518)
+++ trunk/ppSub/src/ppSubReadout.c	(revision 20519)
@@ -350,5 +350,8 @@
             outRO->weight = psImageCopy(outRO->weight, minuend->weight, PS_TYPE_F32);
         }
-        outRO->mask = psImageCopy(outRO->mask, minuend->mask, PS_TYPE_MASK);
+        if (minuend->mask) {
+            outRO->mask = psImageCopy(outRO->mask, minuend->mask, PS_TYPE_MASK);
+        }
+        outRO->data_exists = outCell->data_exists = outCell->parent->data_exists = true;
 
         pmFPAfile *photFile = psMetadataLookupPtr(NULL, config->files, "PSPHOT.INPUT");