Errors with WP_DEBUG enabled

When editing the sidebars for the search page with WP_DEBUG enabled, I get the following notices:

Notice: Undefined index: post_id in /home/.../public_html/wp-content/plugins/wp-page-widget/wp-page-widgets.php on line 1037

Notice: Undefined index: tag_id in /home/.../public_html/wp-content/plugins/wp-page-widget/wp-page-widgets.php on line 1037

This happens for all kinds of widgets.

The line of code causing the issue is the following

if (!$_POST['post_id'] && !$_POST['tag_id'] && !$_POST['search_page'])
  die('-1');

I think it should be sufficient to put a few isset calls before checking the $_POST[...] vars.

Thank you.

https://wordpress.org/plugins/wp-page-widget/