diff -r be944660c56a -r 3d72ae0968f4 wp/wp-includes/SimplePie/Enclosure.php
--- a/wp/wp-includes/SimplePie/Enclosure.php	Wed Sep 21 18:19:35 2022 +0200
+++ b/wp/wp-includes/SimplePie/Enclosure.php	Tue Sep 27 16:37:53 2022 +0200
@@ -1152,7 +1152,12 @@
 		// If we encounter an unsupported mime-type, check the file extension and guess intelligently.
 		if (!in_array($type, array_merge($types_flash, $types_fmedia, $types_quicktime, $types_wmedia, $types_mp3)))
 		{
-			switch (strtolower($this->get_extension()))
+			$extension = $this->get_extension();
+			if ($extension === null) {
+				return null;
+			}
+
+			switch (strtolower($extension))
 			{
 				// Audio mime-types
 				case 'aac':