wp-includes/SimplePie/src/Enclosure.php:754Get all thumbnails
array|null public function get_thumbnails() { if ($this->thumbnails !== null) { return $this->thumbnails; } return null; }One change between 6.7.7 and 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
array|null to string[]|null.verified against sourcesrc/wp-includes/SimplePie/src/Enclosure.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.