Fixed some issues detected by PHPstan.

src/Security/Voter/StructureVoter.php

@@ -54,6 +54,7 @@ class StructureVoter extends ExtendedVoter
             //If permission name is null, then the subject is not supported
             return (null !== $permission_name) && $this->resolver->isValidOperation($permission_name, $attribute);
         }
+        return false;
     }
 
     /**
@@ -94,8 +95,9 @@ class StructureVoter 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
     {