=== Error ===
Request URL: <https://en.wikipedia.org/wiki/Special:Book>
Request ID: `XOwxIgpAAEMAAEWmaxgAAAAP`
```name=message
PHP Notice: Undefined index: subtitle
```
```name=trace (since 1.34-wmf.6),lines=10
#0 /srv/mediawiki/php-1.34.0-wmf.6/extensions/Collection/includes/Specials/SpecialCollection.php(1013): MWExceptionHandler::handleError(integer, string, string, integer, array, array)
#1 /srv/mediawiki/php-1.34.0-wmf.6/extensions/Collection/includes/Specials/SpecialCollection.php(374): SpecialCollection->saveCollection(Title, boolean)
#2 /srv/mediawiki/php-1.34.0-wmf.6/extensions/Collection/includes/Specials/SpecialCollection.php(241): SpecialCollection->processSaveCollectionCommand()
#3 /srv/mediawiki/php-1.34.0-wmf.6/includes/specialpage/SpecialPage.php(570): SpecialCollection->execute(NULL)
#4 /srv/mediawiki/php-1.34.0-wmf.6/includes/specialpage/SpecialPageFactory.php(575): SpecialPage->run(NULL)
#5 /srv/mediawiki/php-1.34.0-wmf.6/includes/MediaWiki.php(288): MediaWiki\Special\SpecialPageFactory->executePath(Title, RequestContext)
#6 /srv/mediawiki/php-1.34.0-wmf.6/includes/MediaWiki.php(865): MediaWiki->performRequest()
#7 /srv/mediawiki/php-1.34.0-wmf.6/includes/MediaWiki.php(515): MediaWiki->main()
#8 /srv/mediawiki/php-1.34.0-wmf.6/index.php(42): MediaWiki->run()
```
```name=trace (upto 1.34-wmf.5),lines=10
#0 /srv/mediawiki/php-1.34.0-wmf.4/extensions/Collection/Collection.body.php(1013): MWExceptionHandler::handleError(integer, string, string, integer, array, array)
#1 /srv/mediawiki/php-1.34.0-wmf.4/extensions/Collection/Collection.body.php(374): SpecialCollection->saveCollection(Title, boolean)
#2 /srv/mediawiki/php-1.34.0-wmf.4/extensions/Collection/Collection.body.php(241): SpecialCollection->processSaveCollectionCommand()
#3 /srv/mediawiki/php-1.34.0-wmf.4/includes/specialpage/SpecialPage.php(569): SpecialCollection->execute(NULL)
#4 /srv/mediawiki/php-1.34.0-wmf.4/includes/specialpage/SpecialPageFactory.php(575): SpecialPage->run(NULL)
#5 /srv/mediawiki/php-1.34.0-wmf.4/includes/MediaWiki.php(288): MediaWiki\Special\SpecialPageFactory->executePath(Title, RequestContext)
#6 /srv/mediawiki/php-1.34.0-wmf.4/includes/MediaWiki.php(865): MediaWiki->performRequest()
#7 /srv/mediawiki/php-1.34.0-wmf.4/includes/MediaWiki.php(515): MediaWiki->main()
#8 /srv/mediawiki/php-1.34.0-wmf.4/index.php(42): MediaWiki->run()
```
=== Impact ===
Unknown.
=== Notes ===
Seen since at least 1.34-wmf.3, possibly longer.
Might be similar to T189636, which affected a different file entry point from the same code base.