PB-166: Page Builder doesn't implement destroy method

Author: omiroshnichenko

app/code/Magento/PageBuilder/view/adminhtml/web/js/stage.js

@@ -160,6 +160,8 @@ export default class Stage {
      * @param params
      */
     private onContentTypeRemoved(params: ContentTypeRemovedParamsInterface): void {
-        params.parentContentType.removeChild(params.contentType);
+        if (params.parentContentType) {
+            params.parentContentType.removeChild(params.contentType);
+        }
     }
 }