Reported by @etonkovidova at https://phabricator.wikimedia.org/T110358#1576773:
"
In betalabs it happens only when a board description has a template(any template) and that template was deleted and 'Save changes' was clicked:
Delete a content from a board descirption.
In wikitext ode - add [[Category:Flow|*]] - click on 'Save description'
"
The following error is displayed:
[32ec9d4d] Exception Caught: Row has null primary key:
```
2015-08-26 19:42:35 deployment-mediawiki02 enwiki exception ERROR: [32ec9d4d] /w/api.php Flow\Exception\DataPersistenceException from line 117 of /srv/mediawiki/php-master/extensions/Flow/includes/Data/Storage/BasicDbStorage.php: Row has null primary key: {"exception":"[Exception Flow\\Exception\\DataPersistenceException] (/srv/mediawiki/php-master/extensions/Flow/includes/Data/Storage/BasicDbStorage.php:117) Row has null primary key:
[stacktrace]
#0 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ObjectManager.php(187): Flow\\Data\\Storage\\BasicDbStorage->remove(array)
#1 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ObjectManager.php(202): Flow\\Data\\ObjectManager->remove(Flow\\Model\\WikiReference, array)
#2 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ManagerGroup.php(97): Flow\\Data\\ObjectManager->multiRemove(array, array)
#3 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ManagerGroup.php(114): Flow\\Data\\ManagerGroup->multiMethod(string, array, array)
#4 /srv/mediawiki/php-master/extensions/Flow/includes/Data/Listener/ReferenceRecorder.php(77): Flow\\Data\\ManagerGroup->multiRemove(array)
#5 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ObjectManager.php(261): Flow\\Data\\Listener\\ReferenceRecorder->onAfterInsert(Flow\\Model\\Header, array, array)
#6 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ObjectManager.php(170): Flow\\Data\\ObjectManager->insert(array, array)
#7 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ObjectManager.php(143): Flow\\Data\\ObjectManager->multiPut(array, array)
#8 /srv/mediawiki/php-master/extensions/Flow/includes/Data/ManagerGroup.php(80): Flow\\Data\\ObjectManager->put(Flow\\Model\\Header, array)
#9 /srv/mediawiki/php-master/extensions/Flow/includes/Block/Header.php(175): Flow\\Data\\ManagerGroup->put(Flow\\Model\\Header, array)
#10 /srv/mediawiki/php-master/extensions/Flow/includes/SubmissionHandler.php(141): Flow\\Block\\HeaderBlock->commit()
#11 /srv/mediawiki/php-master/extensions/Flow/includes/WorkflowLoader.php(66): Flow\\SubmissionHandler->commit(Flow\\Model\\Workflow, array)
#12 /srv/mediawiki/php-master/extensions/Flow/includes/Api/ApiFlowBasePost.php(41): Flow\\WorkflowLoader->commit(array)
#13 /srv/mediawiki/php-master/extensions/Flow/includes/Api/ApiFlow.php(106): Flow\\Api\\ApiFlowBasePost->execute()
#14 /srv/mediawiki/php-master/includes/api/ApiMain.php(1093): Flow\\Api\\ApiFlow->execute()
#15 /srv/mediawiki/php-master/includes/api/ApiMain.php(432): ApiMain->executeAction()
#16 /srv/mediawiki/php-master/includes/api/ApiMain.php(405): ApiMain->executeActionWithErrorHandling()
#17 /srv/mediawiki/php-master/api.php(88): ApiMain->execute()
#18 /srv/mediawiki/w/api.php(3): include(string)
#19 {main}
"}
```
This is probably somehow related to {T107204}