fix: handle order items without GTIN (e.g., vouchers)

Items like vouchers may have no GTIN at all. Previously, the placeholder
product was only created when there were missing GTINs, causing a NOT NULL
constraint violation for items with gtin=None.

Now we also check for items without GTIN and create a placeholder for them.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/services/order_service.py

@@ -480,14 +480,17 @@ class OrderService:
         if isinstance(inventory_units, dict):
             inventory_units = inventory_units.get("nodes", [])
 
-        # Collect all GTINs and validate products exist
+        # Collect all GTINs and check for items without GTINs
         gtins = set()
+        has_items_without_gtin = False
         for unit in inventory_units:
             variant = unit.get("variant", {}) or {}
             trade_id = variant.get("tradeId", {}) or {}
             gtin = trade_id.get("number")
             if gtin:
                 gtins.add(gtin)
+            else:
+                has_items_without_gtin = True
 
         # Batch query all products by GTIN
         products_by_gtin: dict[str, Product] = {}
@@ -507,13 +510,19 @@ class OrderService:
         # Identify missing GTINs (graceful handling - no exception raised)
         missing_gtins = gtins - set(products_by_gtin.keys())
         placeholder = None
-        if missing_gtins:
-            # Get or create placeholder product for unmatched items
+        if missing_gtins or has_items_without_gtin:
+            # Get or create placeholder product for unmatched items or items without GTIN
             placeholder = self._get_or_create_placeholder_product(db, vendor_id)
-            logger.warning(
-                f"Order {order_number}: {len(missing_gtins)} product(s) not found. "
-                f"GTINs: {missing_gtins}. Using placeholder and creating exceptions."
-            )
+            if missing_gtins:
+                logger.warning(
+                    f"Order {order_number}: {len(missing_gtins)} product(s) not found. "
+                    f"GTINs: {missing_gtins}. Using placeholder and creating exceptions."
+                )
+            if has_items_without_gtin:
+                logger.warning(
+                    f"Order {order_number}: Some items have no GTIN. "
+                    f"Using placeholder and creating exceptions."
+                )
 
         # Parse address data
         ship_address = order_data.get("shipAddress", {}) or {}