strnatcasecmp(): Passing null to parameter #2 ($string2) of type string is deprecated

Problem/Motivation

When using PHP 8.1 the following warnings are displayed/logged.

Deprecated function: strnatcasecmp(): Passing null to parameter #2 ($string2) of type string is deprecated in Drupal\Core\Block\BlockManager->Drupal\Core\Plugin\{closure}() (line 97 of core/lib/Drupal/Core/Plugin/CategorizingPluginManagerTrait.php).

Steps to reproduce

Edit layout of any page

Proposed resolution

Prevent passing in NULL by converting it to string.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet