Call to a member function isPublished() on null

Describe your bug or feature request.

We developed a Drupal 11 website for a large bike manufacturer using Drupal Commerce. The bikes on the website are commerce products (variants actually).
The stores that sell this brand are Commerce Stores, and they each have at least one (Drupal) user (a dealer) that can log into the website. When a dealer is logged in, he can order bikes.

The client contacted us that a specific dealer is unable to order bikes.
When I masquerade as this dealer, I can see the error in the logs:

Error: Call to a member function isPublished() on null in Drupal\commerce_cart\CartProvider->isEligibleCart() (regel 263 van /var/www/html/web/modules/contrib/commerce/modules/cart/src/CartProvider.php)

#0 /var/www/html/web/modules/contrib/commerce/modules/cart/src/CartProvider.php(222): Drupal\commerce_cart\CartProvider->isEligibleCart()
#1 /var/www/html/web/modules/contrib/commerce/modules/cart/src/CartProvider.php(161): Drupal\commerce_cart\CartProvider->loadCartData()
#2 /var/www/html/web/modules/contrib/commerce/modules/cart/src/CartProvider.php(148): Drupal\commerce_cart\CartProvider->getCartIds()
#3 /var/www/html/web/modules/contrib/commerce/modules/cart/src/CartLazyBuilders.php(56): Drupal\commerce_cart\CartProvider->getCarts()
#4 [internal function]: Drupal\commerce_cart\CartLazyBuilders->cartBlock()
#5 /var/www/html/web/core/lib/Drupal/Core/Security/DoTrustedCallbackTrait.php(107): call_user_func_array()
#6 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(876): Drupal\Core\Render\Renderer->doTrustedCallback()
#7 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(414): Drupal\Core\Render\Renderer->doCallback()
#8 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(250): Drupal\Core\Render\Renderer->doRender()
#9 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(141): Drupal\Core\Render\Renderer->doRenderRoot()
#10 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(627): Drupal\Core\Render\Renderer->Drupal\Core\Render\{closure}()
#11 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(140): Drupal\Core\Render\Renderer->executeInRenderContext()
#12 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(167): Drupal\Core\Render\Renderer->renderInIsolation()
#13 /var/www/html/web/core/lib/Drupal/Core/Render/Renderer.php(204): Drupal\Core\Render\Renderer->doRenderPlaceholder()
#14 /var/www/html/web/core/modules/big_pipe/src/Render/BigPipe.php(730): Drupal\Core\Render\Renderer->renderPlaceholder()
#15 /var/www/html/web/core/modules/big_pipe/src/Render/BigPipe.php(500): Drupal\big_pipe\Render\BigPipe->renderPlaceholder()
#16 [internal function]: Drupal\big_pipe\Render\BigPipe->Drupal\big_pipe\Render\{closure}()
#17 /var/www/html/web/core/modules/big_pipe/src/Render/BigPipe.php(507): Fiber->start()
#18 /var/www/html/web/core/modules/big_pipe/src/Render/BigPipe.php(256): Drupal\big_pipe\Render\BigPipe->sendPlaceholders()
#19 /var/www/html/web/core/modules/big_pipe/src/Render/BigPipeResponse.php(116): Drupal\big_pipe\Render\BigPipe->sendContent()
#20 /var/www/html/vendor/symfony/http-foundation/Response.php(397): Drupal\big_pipe\Render\BigPipeResponse->sendContent()
#21 /var/www/html/web/index.php(20): Symfony\Component\HttpFoundation\Response->send()
#22 {main}

The lines of code that throws the error looks like this:

    // A cart belonging to an unpublished store should no longer be eligible.
    if (!$cart->getStore()->isPublished()) {
      return FALSE;
    }

I have no idea why getStore returns null, but the error can be fixed by adding an extra check:

    // A cart without valid store should not be valid.
    if (!$cart->getStore()) {
      return FALSE;
    }
    // A cart belonging to an unpublished store should no longer be eligible.
    if (!$cart->getStore()->isPublished()) {
      return FALSE;
    }

I have attached a patch that adds this extra check.