Indexer crash at federated share

NC 14.0.8, FTS 1.1.1, FTS-ES 1.0.3, FTS-Files 1.1.3

while occ fulltextsearch:index the job aborts with the following traceback:

An unhandled exception has been thrown:
TypeError: Argument 1 passed to OC\OCS\DiscoveryService::discover() must be of the type string, null given, called in /srv/www/htdocs/nextcloud/apps/files_sharing/lib/External/Manager.php on line 382 and defined in /srv/www/htdocs/nextcloud/lib/private/OCS/DiscoveryService.php:65
Stack trace:
#0 /srv/www/htdocs/nextcloud/apps/files_sharing/lib/External/Manager.php(382): OC\OCS\DiscoveryService->discover(NULL, 'FEDERATED_SHARI...')
#1 /srv/www/htdocs/nextcloud/apps/files_sharing/lib/External/Manager.php(527): OCA\Files_Sharing\External\Manager->sendFeedbackToRemote(NULL, NULL, NULL, 'decline')
#2 /srv/www/htdocs/nextcloud/apps/files_sharing/lib/External/Storage.php(217): OCA\Files_Sharing\External\Manager->removeShare('e0-e376-1035-94...')
#3 /srv/www/htdocs/nextcloud/apps/files_sharing/lib/External/Storage.php(181): OCA\Files_Sharing\External\Storage->checkStorageAvailability()
#4 /srv/www/htdocs/nextcloud/lib/private/Files/Storage/Wrapper/Wrapper.php(378): OCA\Files_Sharing\External\Storage->hasUpdated('', 1521626402)
#5 /srv/www/htdocs/nextcloud/lib/private/Files/Storage/Wrapper/Availability.php(398): OC\Files\Storage\Wrapper\Wrapper->hasUpdated('', 1521626402)
#6 /srv/www/htdocs/nextcloud/lib/private/Files/Storage/Wrapper/Wrapper.php(378): OC\Files\Storage\Wrapper\Availability->hasUpdated('', 1521626402)
#7 /srv/www/htdocs/nextcloud/lib/private/Files/Storage/Wrapper/Wrapper.php(378): OC\Files\Storage\Wrapper\Wrapper->hasUpdated('', 1521626402)
#8 /srv/www/htdocs/nextcloud/lib/private/Files/Cache/Watcher.php(126): OC\Files\Storage\Wrapper\Wrapper->hasUpdated('', 1521626402)
#9 /srv/www/htdocs/nextcloud/lib/private/Files/View.php(1332): OC\Files\Cache\Watcher->needsUpdate('', Object(OC\Files\Cache\CacheEntry))
#10 /srv/www/htdocs/nextcloud/lib/private/Files/View.php(1374): OC\Files\View->getCacheEntry(Object(OCA\Files_Trashbin\Storage), '', '/02051fe0-e376-...')
#11 /srv/www/htdocs/nextcloud/lib/private/Files/Node/Root.php(198): OC\Files\View->getFileInfo('/02051fe0-e376-...')
#12 /srv/www/htdocs/nextcloud/lib/private/Files/Node/Folder.php(134): OC\Files\Node\Root->get('/02051fe0-e376-...')
#13 /srv/www/htdocs/nextcloud/apps/files_fulltextsearch/lib/Service/FilesService.php(487): OC\Files\Node\Folder->get('SFB Dissipation')
#14 /srv/www/htdocs/nextcloud/apps/files_fulltextsearch/lib/Service/FilesService.php(392): OCA\Files_FullTextSearch\Service\FilesService->updateFilesDocument(Object(OCA\Files_FullTextSearch\Model\FilesDocument))
#15 /srv/www/htdocs/nextcloud/apps/files_fulltextsearch/lib/Provider/FilesProvider.php(285): OCA\Files_FullTextSearch\Service\FilesService->generateDocument(Object(OCA\Files_FullTextSearch\Model\FilesDocument))
#16 /srv/www/htdocs/nextcloud/apps/fulltextsearch/lib/Service/IndexService.php(296): OCA\Files_FullTextSearch\Provider\FilesProvider->fillIndexDocument(Object(OCA\Files_FullTextSearch\Model\FilesDocument))
#17 /srv/www/htdocs/nextcloud/apps/fulltextsearch/lib/Service/IndexService.php(176): OCA\FullTextSearch\Service\IndexService->indexDocuments(Object(OCA\FullTextSearch_ElasticSearch\Platform\ElasticSearchPlatform), Object(OCA\Files_FullTextSearch\Provider\FilesProvider), Array, Object(OCA\FullTextSearch\Model\IndexOptions))
#18 /srv/www/htdocs/nextcloud/apps/fulltextsearch/lib/Command/Index.php(400): OCA\FullTextSearch\Service\IndexService->indexProviderContentFromUser(Object(OCA\FullTextSearch_ElasticSearch\Platform\ElasticSearchPlatform), Object(OCA\Files_FullTextSearch\Provider\FilesProvider), '02051fe0-e376-1...', Object(OCA\FullTextSearch\Model\IndexOptions))
#19 /srv/www/htdocs/nextcloud/apps/fulltextsearch/lib/Command/Index.php(264): OCA\FullTextSearch\Command\Index->indexProvider(Object(OCA\Files_FullTextSearch\Provider\FilesProvider), Object(OCA\FullTextSearch\Model\IndexOptions))
#20 /srv/www/htdocs/nextcloud/3rdparty/symfony/console/Command/Command.php(251): OCA\FullTextSearch\Command\Index->execute(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#21 /srv/www/htdocs/nextcloud/core/Command/Base.php(162): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#22 /srv/www/htdocs/nextcloud/3rdparty/symfony/console/Application.php(946): OC\Core\Command\Base->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#23 /srv/www/htdocs/nextcloud/3rdparty/symfony/console/Application.php(248): Symfony\Component\Console\Application->doRunCommand(Object(OCA\FullTextSearch\Command\Index), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#24 /srv/www/htdocs/nextcloud/3rdparty/symfony/console/Application.php(148): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#25 /srv/www/htdocs/nextcloud/lib/private/Console/Application.php(213): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#26 /srv/www/htdocs/nextcloud/console.php(96): OC\Console\Application->run()
#27 /srv/www/htdocs/nextcloud/occ(11): require_once('/srv/www/htdocs...')
#28 {main}stopping all running indexes

Checkbox 'index external files' is unchecked. Index doesn't get past this error, remains same when I rerun index. (is this setting relevant and really should skip federated shares?)

What can I do to skip inaccessible files, just to finish indexing?

Start with apps/files_sharing/lib/External/Manager.php around lines 382 and 527, then follow apps/files_sharing/lib/External/Storage.php and apps/files_fulltextsearch/lib/Service/FilesService.php. Reproduce with occ fulltextsearch:index and trace the null federated-share data; done means inaccessible federated files no longer abort the indexing run and the remaining files can be indexed.