PHP Fatal error: Uncaught TypeError: array_merge()

[lenasterg]

Hi all.
I have a multisite installation WordPress 6.2, PHP 8.1.
In some subsites, that after switched themes I get the following PHP Fatal error

PHP Fatal error: Uncaught TypeError: array_merge(): Argument #2 must be of type array, null given in /wp-includes/widgets.php:1342

This is caused when executing the line of code
$shown_widgets = array_merge( ...array_values( $sidebars_widgets ) );,
I guess that means that the $sidebars_widgets variable is either null or contains a null value instead of an array.

A fix for that is to add the following two lines

$sidebars_widgets = array_filter($sidebars_widgets);
if ( empty( $sidebars_widgets ) ) {
    return array();
}

before the line :
https://core.trac.wordpress.org/browser/trunk/src/wp-includes/widgets.php#L1342

Bests,
Lena

[jrf]

Thanks @lenasterg for reporting this.

While your proposal fixes the immediate issue, it doesn't address the actual issue, which is "how did that null value get in the $sidebar_widgets array ?"

I think this needs a little deeper investigation and backtracing to figure out what is really going on.

[lenasterg]

Hi @jrf.
I have no clue. It happened on in one subsite, which the user hadn't edited it for more than a year.
During this period, we updated the multisite installation from WP 4.9+ to 6.2.1.
The user can't remember the initial theme, his blog had.

[ironprogrammer]

During test triage review of this ticket, it was agreed that needs-testing-info might help move it forward. Why? This issue may be challenging to reproduce and validate a patch. Also, in the process, additional research and context into what caused the issue might be revealed, as suggested in comment:4.

[hellofromTonya]

The issue of a sidebar's widgets being set to null instead of array is being tracked in #57469. Let's move the discussion and investigation to that ticket to consolidate the effort. Thank you everyone!