From /w/rest.php/war.wikipedia.org/v3/transform/wikitext/to/pagebundle/Zedd as noted in T260082#10557793
Return value of Wikimedia\Parsoid\Config\Env::getDOMFragment() must be an instance of Wikimedia\Parsoid\DOM\DocumentFragment, null returned
from /srv/parsoid-testing/src/Config/Env.php(894)
#0 /srv/parsoid-testing/src/Utils/ContentUtils.php(302): Wikimedia\Parsoid\Config\Env->getDOMFragment(string)
#1 /srv/parsoid-testing/src/Utils/DOMPostOrder.php(32): Wikimedia\Parsoid\Utils\ContentUtils::Wikimedia\Parsoid\Utils\{closure}(Wikimedia\Parsoid\DOM\Element)
#2 /srv/parsoid-testing/src/Utils/ContentUtils.php(312): Wikimedia\Parsoid\Utils\DOMPostOrder::traverse(Wikimedia\Parsoid\DOM\Element, Closure)
#3 /srv/parsoid-testing/src/Utils/ContentUtils.php(365): Wikimedia\Parsoid\Utils\ContentUtils::shiftDSR(Wikimedia\Parsoid\Config\Env, Wikimedia\Parsoid\DOM\Element, Closure, Wikimedia\Parsoid\Ext\ParsoidExtensionAPI)
#4 /srv/parsoid-testing/src/Parsoid.php(582): Wikimedia\Parsoid\Utils\ContentUtils::convertOffsets(Wikimedia\Parsoid\Config\Env, Wikimedia\Parsoid\DOM\Document, string, string)
#5 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Handler/ParsoidHandler.php(753): Wikimedia\Parsoid\Parsoid->pb2pb(MediaWiki\Parser\Parsoid\Config\PageConfig, string, Wikimedia\Parsoid\Core\PageBundle, array)
#6 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Handler/TransformHandler.php(182): MediaWiki\Rest\Handler\ParsoidHandler->wt2html(MediaWiki\Parser\Parsoid\Config\PageConfig, array, string)
#7 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Module/Module.php(415): MediaWiki\Rest\Handler\TransformHandler->execute()
#8 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Module/Module.php(298): MediaWiki\Rest\Module\Module->executeHandler(MWParsoid\Rest\Handler\TransformHandler)
#9 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Router.php(485): MediaWiki\Rest\Module\Module->execute(string, MediaWiki\Rest\RequestFromGlobals)
#10 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Router.php(444): MediaWiki\Rest\Router->doExecute(string, MediaWiki\Rest\RequestFromGlobals)
#11 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/EntryPoint.php(209): MediaWiki\Rest\Router->execute(MediaWiki\Rest\RequestFromGlobals)
#12 /srv/mediawiki/php-1.44.0-wmf.16/includes/MediaWikiEntryPoint.php(202): MediaWiki\Rest\EntryPoint->execute()
#13 /srv/mediawiki/php-1.44.0-wmf.16/rest.php(39): MediaWiki\MediaWikiEntryPoint->run()
#14 /srv/mediawiki/w/rest.php(3): require(string)
#15 {main}PHP Notice: Undefined index: mwf2
exception.trace
from /srv/parsoid-testing/src/Config/Env.php(894)
#0 /srv/parsoid-testing/src/Config/Env.php(894): MWExceptionHandler::handleError(int, string, string, int, array)
#1 /srv/parsoid-testing/src/Utils/ContentUtils.php(302): Wikimedia\Parsoid\Config\Env->getDOMFragment(string)
#2 /srv/parsoid-testing/src/Utils/DOMPostOrder.php(32): Wikimedia\Parsoid\Utils\ContentUtils::Wikimedia\Parsoid\Utils\{closure}(Wikimedia\Parsoid\DOM\Element)
#3 /srv/parsoid-testing/src/Utils/ContentUtils.php(312): Wikimedia\Parsoid\Utils\DOMPostOrder::traverse(Wikimedia\Parsoid\DOM\Element, Closure)
#4 /srv/parsoid-testing/src/Utils/ContentUtils.php(365): Wikimedia\Parsoid\Utils\ContentUtils::shiftDSR(Wikimedia\Parsoid\Config\Env, Wikimedia\Parsoid\DOM\Element, Closure, Wikimedia\Parsoid\Ext\ParsoidExtensionAPI)
#5 /srv/parsoid-testing/src/Parsoid.php(582): Wikimedia\Parsoid\Utils\ContentUtils::convertOffsets(Wikimedia\Parsoid\Config\Env, Wikimedia\Parsoid\DOM\Document, string, string)
#6 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Handler/ParsoidHandler.php(753): Wikimedia\Parsoid\Parsoid->pb2pb(MediaWiki\Parser\Parsoid\Config\PageConfig, string, Wikimedia\Parsoid\Core\PageBundle, array)
#7 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Handler/TransformHandler.php(182): MediaWiki\Rest\Handler\ParsoidHandler->wt2html(MediaWiki\Parser\Parsoid\Config\PageConfig, array, string)
#8 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Module/Module.php(415): MediaWiki\Rest\Handler\TransformHandler->execute()
#9 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Module/Module.php(298): MediaWiki\Rest\Module\Module->executeHandler(MWParsoid\Rest\Handler\TransformHandler)
#10 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Router.php(485): MediaWiki\Rest\Module\Module->execute(string, MediaWiki\Rest\RequestFromGlobals)
#11 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/Router.php(444): MediaWiki\Rest\Router->doExecute(string, MediaWiki\Rest\RequestFromGlobals)
#12 /srv/mediawiki/php-1.44.0-wmf.16/includes/Rest/EntryPoint.php(209): MediaWiki\Rest\Router->execute(MediaWiki\Rest\RequestFromGlobals)
#13 /srv/mediawiki/php-1.44.0-wmf.16/includes/MediaWikiEntryPoint.php(202): MediaWiki\Rest\EntryPoint->execute()
#14 /srv/mediawiki/php-1.44.0-wmf.16/rest.php(39): MediaWiki\MediaWikiEntryPoint->run()
#15 /srv/mediawiki/w/rest.php(3): require(string)
#16 {main}