[wp-trac] [WordPress Trac] #59195: deprecation notice triggered in post.php by passing null to parameter #2 in preg_match()

[WordPress Trac]

#59195: deprecation notice triggered in post.php by passing null to parameter #2 in
preg_match()
-------------------------------------------------+-------------------------
 Reporter:  nosilver4u                           |       Owner:  (none)
     Type:  defect (bug)                         |      Status:  new
 Priority:  normal                               |   Milestone:  Awaiting
                                                 |  Review
Component:  Media                                |     Version:  6.3
 Severity:  normal                               |  Resolution:
 Keywords:  has-patch needs-testing php81        |     Focuses:  php-
  changes-requested                              |  compatibility
-------------------------------------------------+-------------------------

Comment (by nosilver4u):

 I finally figured out where this was coming from. I didn't do a regular
 "trace", but here's the code path:
 wp_match_mime_types() in wp-admin/includes/post.php - 3376
 called by WP_Media_List_Table->get_views()
 which uses the global $avail_post_mime_types, populated by
 wp_edit_attachments_query() called in
 WP_Media_List_Table->prepare_items().
 wp_edit_attachments_query() is in wp-admin/includes/posts.php and runs
 this:
 $avail_post_mime_types = get_available_post_mime_types( 'attachment' );

 The query in get_available_post_mime_types() returns all the distinct
 post_mime_type values from $wpdb->posts. And in my case, there were a pile
 of PDF files with no post_mime_type defined.

 I don't know how that happened, but a bunch of them were from 2018/2016 (I
 already "fixed" them, but could probably dig up a backup if needed).
 So, any attachments with an empty post_mime_type column will trigger this
 bug, as you'll end up with an empty item in the global
 $avail_post_mime_types. Theoretically, it could be fixed by altering the
 SQL, but I'm not sure what the best approach is here.

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Ticket URL: <https://core.trac.wordpress.org/ticket/59195#comment:9>
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