MC-15981: Page Builder Render

Author: davemacaulay

app/code/Magento/PageBuilder/view/adminhtml/templates/stage/render.phtml

@@ -24,7 +24,7 @@
                         return this._data[id] = String(val);
                     },
                     getItem: function (id) {
-                        return this._data.hasOwnProperty(id) ? this._data[id] : undefined;
+                        return this._data.hasOwnProperty(id) ? this._data[id] : null;
                     },
                     removeItem: function (id) {
                         return delete this._data[id];