Subscription not working with NONE data source?

Hi,

I'm trying to use AppSync subscription with a mutation on a none data source. However, it looks like the subscription is not working as AppSync doesn't support subscription on none data source. In this document, it's said that:

The following example shows how to work with GraphQL subscriptions. It doesn't specify a data source because the data source could be AWS Lambda, Amazon DynamoDB, or Amazon Elasticsearch Service.

and there is no mention about none data source.

Could somebody please confirm this? Thank you!