Notice: Undefined index: xxxx in C:\temp\dev\htdocs\wp330\wp-includes\post.php on line 3170

[EmmanuelG]

When displaying an attachment page, the message appears.
xxxx is the ID of the parent post of the attachment

line 3170

if ( null === ( $parent_page = $pages[ $page->post_parent ] ) )

Work-around:

if ( !isset($pages[ $page->post_parent ]) || 
null === ( $parent_page = $pages[ $page->post_parent ] ) )

Build version 18864.

#17670