php-warning running benchmark

Problem/Motivation

When I run server benchmarks I get the following php-warning:
Warning: Undefined array key "" in Drupal\site\Entity\SiteEntity->send()
I haven't had time to further debug where it is originating.

Steps to reproduce

Go to /admin/reports/server-benchmarks and execute the benchmark.

#0 web/core/includes/bootstrap.inc(166): _drupal_error_handler_real()
#1 web/modules/contrib/site/src/Entity/SiteEntity.php(974): _drupal_error_handler()
#2 web/modules/contrib/site/src/Entity/SiteEntity.php(420): Drupal\site\Entity\SiteEntity->send()
#3 web/modules/contrib/site/src/Entity/Bundle/DrupalSiteBundle.php(57): Drupal\site\Entity\SiteEntity->save()
#4 web/modules/contrib/site/src/SiteSelf.php(261): Drupal\site\Entity\Bundle\DrupalSiteBundle->save()
#5 web/modules/contrib/site/src/EventSubscriber/SiteSubscriber.php(78): Drupal\site\SiteSelf->saveEntity()
#6 [internal function]: Drupal\site\EventSubscriber\SiteSubscriber->onKernelResponse()
#7 web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func()
#8 vendor/symfony/http-kernel/HttpKernel.php(214): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch()
#9 vendor/symfony/http-kernel/HttpKernel.php(202): Symfony\Component\HttpKernel\HttpKernel->filterResponse()
#10 vendor/symfony/http-kernel/HttpKernel.php(76): Symfony\Component\HttpKernel\HttpKernel->handleRaw()
#11 web/core/lib/Drupal/Core/StackMiddleware/Session.php(53): Symfony\Component\HttpKernel\HttpKernel->handle()
#12 web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(48): Drupal\Core\StackMiddleware\Session->handle()
#13 web/core/lib/Drupal/Core/StackMiddleware/ContentLength.php(28): Drupal\Core\StackMiddleware\KernelPreHandle->handle()
#14 web/core/modules/big_pipe/src/StackMiddleware/ContentLength.php(32): Drupal\Core\StackMiddleware\ContentLength->handle()
#15 web/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\big_pipe\StackMiddleware\ContentLength->handle()
#16 web/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass()
#17 web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(48): Drupal\page_cache\StackMiddleware\PageCache->handle()
#18 web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(51): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle()
#19 web/core/lib/Drupal/Core/StackMiddleware/AjaxPageState.php(36): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle()
#20 web/core/lib/Drupal/Core/StackMiddleware/StackedHttpKernel.php(51): Drupal\Core\StackMiddleware\AjaxPageState->handle()
#21 web/core/lib/Drupal/Core/DrupalKernel.php(741): Drupal\Core\StackMiddleware\StackedHttpKernel->handle()
#22 web/index.php(19): Drupal\Core\DrupalKernel->handle()
#23 {main}