How to make a graphql request for persisted queries using HttpGraphQlClient in spring graphql?

I have spring boot graphql server side and spring graphql client side applications. The client graphql queries are persisted in graphql-server-side. Now from the graphql-client-side application, how to make the graphql requests using the sha256 hash of the graphql query using HttpGraphQlClient?

I know that we pass the sha256 hash in the 'extensions' key of the request body. But to access RequestSpec's extensions() method, GraphQlClient contract exposes two methods RequestSpec document(String document) and RequestSpec documentName(String document). One way it to do is graphQlClient.document(null).extensions(Map.of(...)).executeSync(), but the parameter for document() method is not nullable so that doesn't work.

Basically, how to make a graphql request with the hash of a persisted query using HttpGraphQlClient? Or is this not supported yet?