“Undefined index” notices because no posts

I get two “Undefined index” notices because, as I assume, my website has no posts but only (a couple of) pages. Commenting out these two lines removes the notices without causing (so far) any other disturbances.
A fine plug-in otherwise.
Notice: Undefined index: post_id in /Volumes/data/sites/mylandyourland.be/wp-content/plugins/pagerestrict/inc/admin.php on line 72
Notice: Undefined variable: post_ids in /Volumes/data/sites/mylandyourland.be/wp-content/plugins/pagerestrict/inc/admin.php on line 81