From 6d2384448336c1b55e335cd0cc8b01085fbaaf99 Mon Sep 17 00:00:00 2001
From: Tim Edwards <tim@opencircuitdesign.com>
Date: Fri, 27 Oct 2023 10:35:27 -0400
Subject: [PATCH] Corrected an error in the flattening routine that will cause
 the "flatten" command to crash if there are black-box subcircuits in the
 netlist.

---
 base/flatten.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/base/flatten.c b/base/flatten.c
index a42e03c..3742931 100644
--- a/base/flatten.c
+++ b/base/flatten.c
@@ -136,17 +136,16 @@ void flattenCell(char *name, int file)
 	    ob2 = ob2->next;
 	}
     
-
       /* delete all port elements from child */
       while (IsPort(ChildObjList)) {
 	/* delete all ports at beginning of list */
 	if (Debug) Printf("deleting leading port from child\n");
 	tmp = ChildObjList->next;
 	FreeObjectAndHash(ChildObjList, ChildCell);
-	ChildObjList = tmp;
+        if ((ChildObjList = tmp) == NULL) break;
       }
       tmp = ChildObjList;
-      while (tmp->next != NULL) {
+      while (tmp && (tmp->next != NULL)) {
 	if (IsPort(tmp->next)) {
 	  ob2 = (tmp->next)->next;
 	  if (Debug) Printf("deleting a port from child\n");