From 2c9ba55c7fbe1c2b33022c2ccb033cf777898a9a Mon Sep 17 00:00:00 2001
From: Jacques Lucke <jacques@blender.org>
Date: Fri, 17 Mar 2023 13:55:01 +0100
Subject: [PATCH] Fix #105849: crash when using link-swap with an existing link

The code didn't check if there was actually a link to displace.
---
 source/blender/editors/space_node/node_relationships.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/source/blender/editors/space_node/node_relationships.cc b/source/blender/editors/space_node/node_relationships.cc
index 6b8c6df9ca5..3b109d8b1e2 100644
--- a/source/blender/editors/space_node/node_relationships.cc
+++ b/source/blender/editors/space_node/node_relationships.cc
@@ -900,7 +900,11 @@ static void displace_links(bNodeTree *ntree, const bNode *node, bNodeLink *inser
   if (linked_socket->is_input()) {
     BLI_assert(!linked_socket->is_multi_input());
     ntree->ensure_topology_cache();
-    bNodeLink *displaced_link = linked_socket->runtime->directly_linked_links.first();
+
+    if (linked_socket->directly_linked_links().is_empty()) {
+      return;
+    }
+    bNodeLink *displaced_link = linked_socket->directly_linked_links().first();
 
     if (!replacement_socket) {
       nodeRemLink(ntree, displaced_link);