wpint: Raise exception if creating shipping label fails for some reason

models/dp_delivery_carrier.py

@@ -195,6 +195,9 @@ class DPDeliveryCarrier(models.Model):
                                   'EUR', customer_reference=pickings.name, contents=wpi_content)
         # actually create the order + download the label
         wpi_res = wpi.api_create_order([wpi_item], 'Max Mustermann')
+        if not 'shipments' in wpi_res:
+            _logger.error("Warenpost International failed to create shipment: %s", wpi_res)
+            raise Warning("Warenpost International failed to create shipment: %s", wpi_res)
         wpi_res_item = wpi_res['shipments'][0]['items'][0]
         png = wpi.api_get_item_label(wpi_res_item['id'], 'image/png')
         # build result dict