From e011fd6b5c1f758557ea5f7e531a35c3fb941295 Mon Sep 17 00:00:00 2001
From: Karl Heuer <kwzh@gnu.org>
Date: Fri, 4 Jun 1999 18:36:35 +0000
Subject: [PATCH] (regexp-opt-group): Avoid infinite recursion on bogus input.

---
 lisp/emacs-lisp/regexp-opt.el | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/regexp-opt.el b/lisp/emacs-lisp/regexp-opt.el
index 589f1b70ac4..6627c20a7bf 100644
--- a/lisp/emacs-lisp/regexp-opt.el
+++ b/lisp/emacs-lisp/regexp-opt.el
@@ -141,7 +141,9 @@ in REGEXP."
 	 (open-charset (if lax "" open-group))
 	 (close-charset (if lax "" close-group)))
     (cond
-     ;;
+     ;; Protect against user-stupidity... could call error here
+     ((null strings)
+      nil)
      ;; If there is only one string, just return it.
      ((= (length strings) 1)
       (if (= (length (car strings)) 1)
-- 
2.39.5