Issue #3240955 by andypost:...

Issue #3240955 by andypost: \Drupal\media\Plugin\Filter\MediaEmbed::applyPerEmbedMediaOverrides() triggers deprecations in PHP 8.1

core/modules/media/src/Plugin/Filter/MediaEmbed.php

@@ -463,7 +463,7 @@ protected function applyPerEmbedMediaOverrides(\DOMElement $node, MediaInterface
         // explicitly empty instead so it can be ignored by assistive
         // technologies, such as screen readers.
         if ($node->getAttribute('alt') === '""') {
-          $node->setAttribute('alt', NULL);
+          $node->setAttribute('alt', '');
         }
         $media->{$image_field}->alt = $node->getAttribute('alt');
         // All media entities have a thumbnail. In the case of image media, it