From c44732ac58befabf0d6f72f2dae0005ffef7d3c4 Mon Sep 17 00:00:00 2001
From: antirez <antirez@gmail.com>
Date: Tue, 28 Nov 2017 18:25:14 +0100
Subject: adlist: fix listJoin() in the case the second list is empty.

See #4192, the original PR removed lines of code that are actually
needed, so thanks to @chunqiulfq for reporting the problem, but merging
solution from @jeesyn after checking, together with @artix75, that the
logic covers all the cases.
---
 src/adlist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/adlist.c b/src/adlist.c
index e87d25cee..ec5f8bbf4 100644
--- a/src/adlist.c
+++ b/src/adlist.c
@@ -353,7 +353,7 @@ void listJoin(list *l, list *o) {
     else
         l->head = o->head;
 
-    l->tail = o->tail;
+    if (o->tail) l->tail = o->tail;
     l->len += o->len;
 
     /* Setup other as an empty list. */
-- 
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