getVoteOwner return null when nested paragraphs

         if ($entity instanceof EntityOwnerInterface) {
-          return $entity->getOwner();
+          $owner = $entity->getOwner();
+          if (is_null($owner) && $entity instanceof ParagraphInterface) {
+            return \Drupal::currentUser();
+          }
+          return $owner;
         }

If an entity type implements the EntityOwnerInterface, it must have a getOwner() method, and that getOwner() method must return a UserInterface. NULL is not a valid return value for getOwner(). See https://api.drupal.org/api/drupal/core!modules!user!src!EntityOwnerInter...

So the issue here is that the Paragraphs module does not return the proper value from getOwner().

Regardless, adding code to special-case paragraph entities would not be an acceptable solution.