Adding forms of custom entities are broken

1. Create new custom content entity (or you can use Group entity from Group module)
2. Configure metatags for this entity, add [entity:url] for example.
3. Go to the group add page
4. Aaaand it's gone.

The website encountered an unexpected error. Please try again later.Drupal\Core\Entity\EntityMalformedException: The "group" entity cannot have a URI as it does not have an ID in Drupal\Core\Entity\Entity->toUrl() (line 180 of core/lib/Drupal/Core/Entity/Entity.php).

group_tokens('group', Array, Array, Array, Object)
call_user_func_array('group_tokens', Array) (Line: 402)
Drupal\Core\Extension\ModuleHandler->invokeAll('tokens', Array) (Line: 304)
Drupal\Core\Utility\Token->generate('group', Array, Array, Array, Object) (Line: 196)
Drupal\Core\Utility\Token->replace('[group:url]', Array, Array) (Line: 48)
Drupal\metatag\MetatagToken->replace('[group:url]', Array, Array) (Line: 496)
Drupal\metatag\MetatagManager->generateRawElements(Array, Object) (Line: 425)
Drupal\metatag\MetatagManager->generateElements(Array, Object) (Line: 409)
metatag_get_tags_from_route() (Line: 113)
metatag_page_attachments(Array) (Line: 297)
Drupal\Core\Render\MainContent\HtmlRenderer->invokePageAttachmentHooks(Array) (Line: 273)
Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object, Object) (Line: 117)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object, Object) (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object, 'kernel.view', Object) (Line: 108)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object) (Line: 158)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 657)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

So, I guess that Metatag module should not generate meta tags for not existing entities yet.