\Drupal\media\Plugin\Filter\MediaEmbed::applyPerEmbedMediaOverrides() triggers deprecations in PHP 8.1

Problem/Motivation

\Drupal\media\Plugin\Filter\MediaEmbed::applyPerEmbedMediaOverrides() could use to pass NULL to DOMElement::setAttribute()

see https://3v4l.org/IWGqr

$doc = new DOMDocument("1.0");
$node = $doc->createElement("para");
$newnode = $doc->appendChild($node);
$newnode->setAttribute("align", NULL);
var_dump($newnode->getAttribute("align"));

Fix from https://git.drupalcode.org/project/drupal/-/commit/a27bd8682c4eb5d87a55e...

Steps to reproduce

Run core/modules/media/tests/src/Kernel/MediaEmbedFilterTest.php on PHP 8.1

From testOverridesAltAndTitle()

  2x: DOMElement::setAttribute(): Passing null to parameter #2 ($value) of type string is deprecated
    2x in MediaEmbedFilterTest::testOverridesAltAndTitle from Drupal\Tests\media\Kernel

Proposed resolution

Pass empty string instead

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet