Spotted while deploying 1.32.0-wmf.20 to group1:
```
5 Notice: serialize(): "" returned as member variable from __sleep() but does not exist in /srv/mediawiki/php-1.32.0-wmf.19/includes/objectcache/SqlBagOStuff.php on line 668
5 Notice: serialize(): "" returned as member variable from __sleep() but does not exist in /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php on line 225
5 Notice: serialize(): "" returned as member variable from __sleep() but does not exist
```
That might come from objects coming from the cache that do not match the object signature in the code?
Example with exception id W4-U9QpAAEIAADo3ElYAAAAN
```
PHP Notice: serialize(): "" returned as member variable from __sleep() but does not exist
#0 [internal function]: MWExceptionHandler::handleError(integer, string, string, integer, array, array)
#1 [internal function]: Memcached->setByKey(string, string, ParserOutput, integer)
#2 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MemcachedBagOStuff.php(65): Memcached->set(string, ParserOutput, integer)
#3 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MemcachedPeclBagOStuff.php(162): MemcachedBagOStuff->set(string, ParserOutput, integer)
#4 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php(232): MemcachedPeclBagOStuff->set(string, ParserOutput, integer)
#5 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php(139): MultiWriteBagOStuff->doWrite(array, boolean, string, string, ParserOutput, integer)
#6 /srv/mediawiki/php-1.32.0-wmf.19/includes/parser/ParserCache.php(336): MultiWriteBagOStuff->set(string, ParserOutput, integer)
#7 /srv/mediawiki/php-1.32.0-wmf.19/includes/Storage/DerivedPageDataUpdater.php(1402): ParserCache->save(ParserOutput, WikiPage, ParserOptions, string, integer)
#8 /srv/mediawiki/php-1.32.0-wmf.19/includes/Storage/PageUpdater.php(1199): MediaWiki\Storage\DerivedPageDataUpdater->doUpdates()
#9 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/rdbms/database/Database.php(3746): Closure$MediaWiki\Storage\PageUpdater::getAtomicSectionUpdate(Wikimedia\Rdbms\DatabaseMysqli, string)
#10 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/rdbms/database/DBConnRef.php(49): Wikimedia\Rdbms\Database->doAtomicSection(string, Closure$MediaWiki\Storage\PageUpdater::getAtomicSectionUpdate;1380)
#11 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/rdbms/database/DBConnRef.php(529): Wikimedia\Rdbms\DBConnRef->__call(string, array)
#12 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/AtomicSectionUpdate.php(35): Wikimedia\Rdbms\DBConnRef->doAtomicSection(string, Closure$MediaWiki\Storage\PageUpdater::getAtomicSectionUpdate;1380)
#13 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(268): AtomicSectionUpdate->doUpdate()
#14 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(214): DeferredUpdates::runUpdate(AtomicSectionUpdate, Wikimedia\Rdbms\LBFactoryMulti, string, integer)
#15 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(130): DeferredUpdates::execute(array, string, integer)
#16 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(607): DeferredUpdates::doUpdates(string, integer)
#17 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(576): MediaWiki::preOutputCommit(RequestContext, Closure$MediaWiki::main;343)
#18 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(884): MediaWiki->doPreOutputCommit(Closure$MediaWiki::main;343)
#19 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(525): MediaWiki->main()
#20 /srv/mediawiki/php-1.32.0-wmf.19/index.php(42): MediaWiki->run()
#21 /srv/mediawiki/w/index.php(3): include(string)
#22 {main}
```
```
PHP Notice: serialize(): "" returned as member variable from __sleep() but does not exist
/srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php:225
#0 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php(225): MWExceptionHandler::handleError(integer, string, string, integer, array, array)
#1 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php(139): MultiWriteBagOStuff->doWrite(array, boolean, string, string, ParserOutput, integer)
#2 /srv/mediawiki/php-1.32.0-wmf.19/includes/parser/ParserCache.php(336): MultiWriteBagOStuff->set(string, ParserOutput, integer)
#3 /srv/mediawiki/php-1.32.0-wmf.19/includes/Storage/DerivedPageDataUpdater.php(1402): ParserCache->save(ParserOutput, WikiPage, ParserOptions, string, integer)
#4 /srv/mediawiki/php-1.32.0-wmf.19/includes/Storage/PageUpdater.php(1199): MediaWiki\Storage\DerivedPageDataUpdater->doUpdates()
#5 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/rdbms/database/Database.php(3746): Closure$MediaWiki\Storage\PageUpdater::getAtomicSectionUpdate(Wikimedia\Rdbms\DatabaseMysqli, string)
#6 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/rdbms/database/DBConnRef.php(49): Wikimedia\Rdbms\Database->doAtomicSection(string, Closure$MediaWiki\Storage\PageUpdater::getAtomicSectionUpdate;1380)
#7 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/rdbms/database/DBConnRef.php(529): Wikimedia\Rdbms\DBConnRef->__call(string, array)
#8 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/AtomicSectionUpdate.php(35): Wikimedia\Rdbms\DBConnRef->doAtomicSection(string, Closure$MediaWiki\Storage\PageUpdater::getAtomicSectionUpdate;1380)
#9 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(268): AtomicSectionUpdate->doUpdate()
#10 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(214): DeferredUpdates::runUpdate(AtomicSectionUpdate, Wikimedia\Rdbms\LBFactoryMulti, string, integer)
#11 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(130): DeferredUpdates::execute(array, string, integer)
#12 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(607): DeferredUpdates::doUpdates(string, integer)
#13 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(576): MediaWiki::preOutputCommit(RequestContext, Closure$MediaWiki::main;343)
#14 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(884): MediaWiki->doPreOutputCommit(Closure$MediaWiki::main;343)
#15 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(525): MediaWiki->main()
#16 /srv/mediawiki/php-1.32.0-wmf.19/index.php(42): MediaWiki->run()
#17 /srv/mediawiki/w/index.php(3): include(string)
#18 {main}
```
```
/srv/mediawiki/php-1.32.0-wmf.19/includes/objectcache/SqlBagOStuff.php:668
PHP Notice: serialize(): "" returned as member variable from __sleep() but does not exist
#0 /srv/mediawiki/php-1.32.0-wmf.19/includes/objectcache/SqlBagOStuff.php(668): MWExceptionHandler::handleError(integer, string, string, integer, array, array)
#1 /srv/mediawiki/php-1.32.0-wmf.19/includes/objectcache/SqlBagOStuff.php(351): SqlBagOStuff->serialize(ParserOutput)
#2 /srv/mediawiki/php-1.32.0-wmf.19/includes/objectcache/SqlBagOStuff.php(376): SqlBagOStuff->setMulti(array, integer)
#3 /srv/mediawiki/php-1.32.0-wmf.19/includes/libs/objectcache/MultiWriteBagOStuff.php(240): SqlBagOStuff->set(string, ParserOutput, integer)
#4 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/MWCallableUpdate.php(34): Closure$MultiWriteBagOStuff::doWrite()
#5 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(268): MWCallableUpdate->doUpdate()
#6 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(214): DeferredUpdates::runUpdate(MWCallableUpdate, Wikimedia\Rdbms\LBFactoryMulti, string, integer)
#7 /srv/mediawiki/php-1.32.0-wmf.19/includes/deferred/DeferredUpdates.php(134): DeferredUpdates::execute(array, string, integer)
#8 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(914): DeferredUpdates::doUpdates(string)
#9 /srv/mediawiki/php-1.32.0-wmf.19/includes/MediaWiki.php(734): MediaWiki->restInPeace(string, boolean)
#10 [internal function]: Closure$MediaWiki::doPostOutputShutdown()
#11 {main}
```