In `@src/Sylius/Bundle/ShopBundle/Controller/CartSummaryController.php`:
- Around line 46-47: The form created in CartSummaryController uses
$this->formFactory->createNamed('', $formType ?? CartType::class) but isn’t
bound to the current cart, so bind the cart as the third argument: pass $cart to
createNamed() (i.e., $this->formFactory->createNamed('', $formType ??
CartType::class, $cart)) so the form can access and submit cart data correctly.

In `@UPGRADE-2.3.md`:
- Around line 64-66: The example override sets the sylius_shop_cart_summary
route path incorrectly to "/thank-you"; update the route declaration for
sylius_shop_cart_summary so its path remains "/" (i.e., change path: /thank-you
to path: /) to reflect the correct cart summary route in the documentation.

In `@src/Sylius/Bundle/ShopBundle/Controller/CartSummaryAction.php`:
- Line 46: The form is created with $this->formFactory->createNamed('',
$formType ?? CartType::class) but no data, so the form isn't bound to the
current cart; modify the call to pass the cart as the data argument so the form
is built with the actual cart contents (use $cart as the second/third parameter
depending on overload), i.e. update the createNamed invocation in
CartSummaryAction to include $cart when creating the form (reference:
createNamed, $formFactory, CartType, $cart).

In `@src/Sylius/Bundle/ShopBundle/Resources/config/routing/order.yml`:
- Around line 4-9: The route definition sylius_shop_order_thank_you contains an
empty defaults: key which YAML parses as null and causes a Symfony route-loading
TypeError; fix it by either removing the empty defaults: line entirely or
initializing it as an empty mapping (defaults: {}) in the
sylius_shop_order_thank_you route definition so Symfony receives an array of
defaults.