We have a local installation of Pressbooks that’s been around for years. It recently updated to WordPress 6.3.1 and one of our Pressbooks admin reported that attempting to view the Users screen generates a WordPress critical error. “Network Admin” or “Pressbooks” → “Users” → “All Users”
Fatal error: Uncaught Error: Attempt to modify property “fields” on null in /code/wp-content/plugins/pressbooks/symbionts/custom-metadata/custom_metadata.php:868 Stack trace: #0 /code/wp-content/plugins/pressbooks/symbionts/custom-metadata/custom_metadata.php(440): custom_metadata_manager->_push_field(‘pb_title’, Object(stdClass), ‘general-book-in…’, ‘metadata’) #1 /code/wp-content/plugins/pressbooks/symbionts/custom-metadata/custom_metadata.php(358): custom_metadata_manager->add_field_to_group(‘pb_title’, Object(stdClass), ‘general-book-in…’, Array) #2 /code/wp-content/plugins/pressbooks/symbionts/custom-metadata/custom_metadata.php(1488): custom_metadata_manager->add_metadata_field(‘pb_title’, ‘metadata’, Array) #3 /code/wp-content/plugins/pressbooks/inc/admin/metaboxes/namespace.php(187): x_add_metadata_field(‘pb_title’, ‘metadata’, Array) #4 /code/wp-includes/class-wp-hook.php(310): Pressbooks\Admin\Metaboxes\add_meta_boxes(‘user’) #5 /code/wp-includes/class-wp-hook.php(334): WP_Hook->apply_filters(‘’, Array) #6 /code/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #7 /code/wp-content/plugins/pressbooks/symbionts/custom-metadata/custom_metadata.php(192): do_action(‘custom_metadata…’, ‘user’) #8 /code/wp-includes/class-wp-hook.php(310): custom_metadata_manager->init_metadata(‘’) #9 /code/wp-includes/class-wp-hook.php(334): WP_Hook->apply_filters(‘’, Array) #10 /code/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #11 /code/wp-admin/admin.php(385): do_action(‘load-users.php’) #12 /code/wp-admin/users.php(11): require_once(‘/code/wp-admin/…’) #13 {main} thrown in /code/wp-content/plugins/pressbooks/symbionts/custom-metadata/custom_metadata.php on line 868
WordPress Configuration
Network Type: Subdirectory
Version: 6.3.1
Language: en_US
WP_ENV: Not set
WP_DEBUG: Disabled
Memory Limit: 64M
Pressbooks Configuration
Version: 5.16.0
Root Theme: Aldine
Root Theme Version: 1.6.4
Server Configuration
PHP Version: 8.1.23
MySQL Version: 5.5.30
Webserver Info: nginx/1.25.2
PHP Configuration
Safe Mode: Disabled
Memory Limit: 256M
Upload Max Size: 100M
Post Max Size: 100M
Upload Max Filesize: 100M
Time Limit: 120
Max Input Vars: 10000
URL-aware fopen: On (1)
Display Errors: On (1)
PHP Extensions
OPcache: Zend
XDebug: Disabled
cURL: Supported
cURL Version: 7.61.1
imagick: Installed
xsl: Installed
It looks like “Add New” works OK.