Ticket #38271: 38271.2.diff

src/wp-admin/js/post.js

@@ -105 +105 @@
          * Overwrite the content of the Featured Image postbox
          *
          * @param {string} html New HTML to be displayed in the content area of the postbox.
-         * 
+         *
          * @global
          */
         WPSetThumbnailHTML = function(html){
@@ -506 +506 @@
                         active_post_lock: $('#active_post_lock').val()
                 };
 
+                if ( 'undefined' === typeof data.active_post_lock ) {
+                        return;
+                }
+
                 if (window.FormData && window.navigator.sendBeacon) {
                         var formData = new window.FormData();