3023322 - Contextual Links Style Update

Closes #3023322

core/lib/Drupal/Core/File/MimeType/MimeTypeGuesser.php

@@ -73,6 +73,8 @@ public function guessMimeType(string $path) : ?string {
         return $mime_type;
       }
     }
+
+    return NULL;
   }
 
   /**