Undefined array key in widgets.php on line 919

[sageth]

If you enable a plugin with a widget and then go to a page which does not display the widget (e.g. a Jetpack sitemap), you will receive an error similar to:
PHP message: PHP Warning: Undefined array key "jetpack-search-filters-1" in /wp-includes/widgets.php on line 918
PHP message: PHP Warning: Trying to access array offset on value of type null in /wp-includes/widgets.php on line 918" while reading response header from upstream, ...,
request: "GET /attachment-sitemap4.xml HTTP/2.0", ...,
referrer: "/sitemap_index.xml"

The issue appears to occur with some plugins, but not all and adding a check to see if the variable is set first seems to address the issue. There is no identified front-end impact, however, this can quickly fill up logs depending on your site traffic and configuration.

Testing can be completed by using Jetpack Search and Rank Math Sitemap xml files, though other combinations exist.

In some cases, viewing a page or post will cause a PHP warning:

PHP Warning: Trying to access array offset on value of type null in /wp-includes/widgets.php on line 918" while reading response header from upstream, ...,
request: "GET /attachment-sitemap4.xml HTTP/2.0", ...,
referrer: "/sitemap_index.xml"

This appears to be a logging issue only.

Description of Change: Adding a check to see if the widget ID is set prior to evaluation.

Trac ticket: https://core.trac.wordpress.org/ticket/57518