JSON:API breaks after installing OpenAPI

After installing OpenAPI module - https://www.drupal.org/project/openapi - navigating to /jsonapi produces this error:

Error: Call to a member function getEntityTypeId() on null in Drupal\jsonapi\EventSubscriber\ResourceResponseValidator->validateResponse() (line 212 of /var/www/html/web/modules/contrib/jsonapi/src/EventSubscriber/ResourceResponseValidator.php) 
	#0 /var/www/html/web/modules/contrib/jsonapi/src/EventSubscriber/ResourceResponseValidator.php(151): Drupal\jsonapi\EventSubscriber\ResourceResponseValidator->validateResponse(Object(Drupal\Core\Cache\CacheableResponse), Object(Symfony\Component\HttpFoundation\Request)) 
	#1 /var/www/html/web/modules/contrib/jsonapi/src/EventSubscriber/ResourceResponseValidator.php(141): Drupal\jsonapi\EventSubscriber\ResourceResponseValidator->doValidateResponse(Object(Drupal\Core\Cache\CacheableResponse), Object(Symfony\Component\HttpFoundation\Request)) 
	#2 [internal function]: Drupal\jsonapi\EventSubscriber\ResourceResponseValidator->onResponse(Object(Symfony\Component\HttpKernel\Event\FilterResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher)) 
	#3 /var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): call_user_func(Array, Object(Symfony\Component\HttpKernel\Event\FilterResponseEvent), 'kernel.response', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher)) 
	#4 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(191): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.response', Object(Symfony\Component\HttpKernel\Event\FilterResponseEvent)) 
	#5 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(173): Symfony\Component\HttpKernel\HttpKernel->filterResponse(Object(Drupal\jsonapi\ResourceResponse), Object(Symfony\Component\HttpFoundation\Request), 1) 
	#6 /var/www/html/vendor/symfony/http-kernel/HttpKernel.php(68): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) 
	#7 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#8 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#9 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(106): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#10 /var/www/html/web/core/modules/page_cache/src/StackMiddleware/PageCache.php(85): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#11 /var/www/html/web/modules/contrib/jsonapi/src/StackMiddleware/FormatSetter.php(45): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#12 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\jsonapi\StackMiddleware\FormatSetter->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#13 /var/www/html/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(52): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#14 /var/www/html/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#15 /var/www/html/web/core/lib/Drupal/Core/DrupalKernel.php(693): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) 
	#16 /var/www/html/web/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) 
	#17 {main}.