Index: trunk/ppStack/src/ppStackLoop.c
===================================================================
--- trunk/ppStack/src/ppStackLoop.c	(revision 17642)
+++ trunk/ppStack/src/ppStackLoop.c	(revision 17682)
@@ -494,4 +494,7 @@
             while ((item = psMetadataGetAndIncrement(iter))) {
                 psPixels *pixels = item->data.V; // Rejected pixels
+                if (!pixels) {
+                    continue;
+                }
                 psTrace("ppStack", 5, "Adding %ld pixels to inspect to image %d", pixels->n, i);
                 inspect = psPixelsConcatenate(inspect, pixels);