Error on Settings page

The plugin is working fine, so this is mostly a cosmetic error.

In Settings > Post Expirator > Defaults, I see an error under Taxonomy (hierarchical) for pages and some custom post types:
Notice: Undefined index: taxonomy in /…/wp-content/plugins/post-expirator/post-expirator.php on line 891

This is not surprising as they have no taxonomy set. But it would be nice to check for taxonomy and omit that entire section if it does not exist.