Task #3362585: PHP 8.1 deprecation notice for passing NULL to explode()

Authored-by: frob <14631-frob@users.noreply.drupalcode.org>
Reviewed-by: dww <git@dwwright.net>

(cherry picked from commit 02161dc8)

pathologic.module

@@ -46,7 +46,7 @@ function _pathologic_filter($text, $settings, $hash) {
   $cached_settings = &drupal_static(__FUNCTION__, []);
   if (!isset($cached_settings[$hash])) {
     $settings['local_paths_exploded'] = [];
-    if ($settings['local_paths'] !== '') {
+    if ($settings['local_paths'] ?? '' !== '') {
       // Build an array of the exploded local paths for this format's settings.
       // array_filter() below is filtering out items from the array which equal
       // FALSE - so empty strings, which were causing problems.