notification-hub: avoid false failure on gcm update output

AAZ output shaping no longer requires properties.gcmCredential; return {} when missing to avoid ResourceNotFoundError.

Author: a0x1ab

src/notification-hub/azext_notification_hub/aaz/latest/notification_hub/credential/gcm/_create.py

@@ -92,7 +92,9 @@ def post_instance_create(self, instance):
         pass
 
     def _output(self, *args, **kwargs):
-        result = self.deserialize_output(self.ctx.selectors.subresource.required(), client_flatten=True)
+        result = self.deserialize_output(self.ctx.selectors.subresource.get(), client_flatten=True)
+        if result is None or result == AAZUndefined:
+            return {}
         return result
 
     class SubresourceSelector(AAZJsonSelector):