Deprecated function: mb_strtolower(): Passing null to parameter #1 ($string) of type string is deprecated

Problem/Motivation

In PHP 8.1, calling the mb_strtolower() function with a null argument returns a deprecation error.

Deprecated function: mb_strtolower(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\block_exclude_pages\Plugin\Condition\BlockExcludePagesRequestPath->evaluate() (line 70 of block_exclude_pages/src/Plugin/Condition/BlockExcludePagesRequestPath.php)

Proposed resolution

We need to ensure the variable is not null.
$pages = mb_strtolower($this->configuration['pages'] ?? '');