PlaceOrderOutput.errors is nullable since Magento 2.4.9

.changeset/place-order-errors-nullable.md

@@ -0,0 +1,5 @@
+---
+'@graphcommerce/magento-graphql': patch
+---
+
+Relax `PlaceOrderOutput.errors` to nullable in the unified schema. Magento 2.4.9 / MageOS 3.2.0 changed the field from `[PlaceOrderError]!` to `[PlaceOrderError]` and returns `null` when the order is placed successfully, so a storefront configured with `magentoVersion` < 249 talking to a 2.4.9 backend failed every successful order with `Cannot return null for non-nullable field PlaceOrderOutput.errors.`

packages/magento-graphql/schema-249/PlaceOrderOutput.graphqls

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+# Magento 2.4.9 (and MageOS 3.2.0) relaxed `PlaceOrderOutput.errors` from
+# `[PlaceOrderError]!` to `[PlaceOrderError]` and now returns `null` when the
+# order is placed successfully. The unified schema must use the nullable
+# variant, otherwise the mesh throws "Cannot return null for non-nullable field
+# PlaceOrderOutput.errors." on every successful placeOrder once the backend
+# runs 2.4.9, while a 2.4.8 backend still satisfies the relaxed contract.
+type PlaceOrderOutput {
+  """
+  An array of place order errors. Returns null on success since Magento 2.4.9.
+  """
+  errors: [PlaceOrderError]
+}