From 9feedd0b0d4be68ca741533e478e1654f2c57165 Mon Sep 17 00:00:00 2001
From: Sergey Biryukov <sergeybiryukov@git.wordpress.org>
Date: Wed, 24 Jan 2018 22:30:12 +0000
Subject: [PATCH] Upgrade/Install: In `postMessage` events handler, check for
 `message` object existence before checking its `action` property.

Props manikmist09.
Fixes #43005.

git-svn-id: https://develop.svn.wordpress.org/trunk@42604 602fd350-edb4-49c9-b593-d223f7449a82
---
 src/wp-admin/js/updates.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/wp-admin/js/updates.js b/src/wp-admin/js/updates.js
index ac360dae8a..7bb1167f6c 100644
--- a/src/wp-admin/js/updates.js
+++ b/src/wp-admin/js/updates.js
@@ -2423,7 +2423,7 @@
 				return;
 			}
 
-			if ( 'undefined' === typeof message.action ) {
+			if ( ! message || 'undefined' === typeof message.action ) {
 				return;
 			}