When I visited to https://testwiki.wiki/wiki/Newsletter:Administrators%27_newsletter , an error was shown as:
[546dfe3595a23adc386955d3] /wiki/Newsletter:Administrators%27_newsletter MWContentSerializationException: The Newsletter content is invalid.
Backtrace:
from /var/www/html/extensions/Newsletter/includes/Content/NewsletterContentHandler.php(72)
#0 /var/www/html/includes/Revision/RevisionStore.php(1245): MediaWiki\Extension\Newsletter\Content\NewsletterContentHandler->unserializeContent()
#1 /var/www/html/includes/Revision/RevisionStore.php(1525): MediaWiki\Revision\RevisionStore->loadSlotContent()
#2 [internal function]: MediaWiki\Revision\RevisionStore->MediaWiki\Revision\{closure}()
#3 /var/www/html/includes/Revision/SlotRecord.php(324): call_user_func()
#4 /var/www/html/includes/Revision/RevisionRecord.php(184): MediaWiki\Revision\SlotRecord->getContent()
#5 /var/www/html/includes/Revision/RenderedRevision.php(233): MediaWiki\Revision\RevisionRecord->getContentOrThrow()
#6 /var/www/html/includes/Revision/RevisionRenderer.php(239): MediaWiki\Revision\RenderedRevision->getSlotParserOutput()
#7 /var/www/html/includes/Revision/RevisionRenderer.php(172): MediaWiki\Revision\RevisionRenderer->combineSlotOutput()
#8 [internal function]: MediaWiki\Revision\RevisionRenderer->MediaWiki\Revision\{closure}()
#9 /var/www/html/includes/Revision/RenderedRevision.php(199): call_user_func()
#10 /var/www/html/includes/poolcounter/PoolWorkArticleView.php(106): MediaWiki\Revision\RenderedRevision->getRevisionParserOutput()
#11 /var/www/html/includes/poolcounter/PoolWorkArticleView.php(77): MediaWiki\PoolCounter\PoolWorkArticleView->renderRevision()
#12 /var/www/html/includes/poolcounter/PoolCounterWork.php(171): MediaWiki\PoolCounter\PoolWorkArticleView->doWork()
#13 /var/www/html/includes/page/ParserOutputAccess.php(362): MediaWiki\PoolCounter\PoolCounterWork->execute()
#14 /var/www/html/includes/page/Article.php(827): MediaWiki\Page\ParserOutputAccess->getParserOutput()
#15 /var/www/html/includes/page/Article.php(547): Article->generateContentOutput()
#16 /var/www/html/includes/actions/ViewAction.php(78): Article->view()
#17 /var/www/html/includes/actions/ActionEntryPoint.php(733): ViewAction->show()
#18 /var/www/html/includes/actions/ActionEntryPoint.php(510): MediaWiki\Actions\ActionEntryPoint->performAction()
#19 /var/www/html/includes/actions/ActionEntryPoint.php(146): MediaWiki\Actions\ActionEntryPoint->performRequest()
#20 /var/www/html/includes/MediaWikiEntryPoint.php(200): MediaWiki\Actions\ActionEntryPoint->execute()
#21 /var/www/html/index.php(58): MediaWiki\MediaWikiEntryPoint->run()
#22 {main}
Please kindly fix this error, thanks.