Fixed some issues detected by PHPstan.

src/Security/Voter/AttachmentVoter.php

@@ -34,14 +34,17 @@ class AttachmentVoter extends ExtendedVoter
      * Similar to voteOnAttribute, but checking for the anonymous user is already done.
      * The current user (or the anonymous user) is passed by $user.
      *
-     * @param $attribute
-     * @param $subject
+     * @param string $attribute
+     * @param mixed $subject
+     * @return bool
      */
     protected function voteOnUser($attribute, $subject, User $user): bool
     {
         if ($subject instanceof Attachment) {
             return $this->resolver->inherit($user, 'parts_attachments', $attribute) ?? false;
         }
+
+        return false;
     }
 
     /**