GraphQLMultiQueryRequest is not serializing variable references

GraphQLMultiQueryRequest is not giving the variable references when serializing. Although GraphQLQueryRequest is serializing correctly. For example I have below schema:

type Query {
    books(author: String): [Book]
    authors: [Author]
}

type Book {
    id: ID
    name: String!
    authors: [Author!]!
}
type Author {
    name: String!
}

The generated DTO's for queries and projections, and the multi-query request will be:

var booksGraphqlQuery = BooksGraphQLQuery.newRequest().authorReference("authorName").build();
var authorsGraphqlQuery = AuthorsGraphQLQuery.newRequest().build();
var booksProjection = BooksProjectionRoot<>().id().name().authors().name();
var authorsProjection = AuthorsProjectionRoot<>().name();

var booksRequest = new GraphQLQueryRequest(booksGraphqlQuery, booksProjection);
var authorsRequest = new GraphQLQueryRequest(authorsGraphqlQuery, authorsProjection);

var multiQueryRequest = new GraphQLMultiQueryRequest(List.of(booksRequest, authorsRequest));

Now if I do booksRequest.serialize(), I see the result query string contains variable references

query ($authorName: String!) {
    books(author: $authorName) {
        id
        name
        authors {
            name
        }
    }
}

But if I do multiQueryRequest.serialize(), then the result query string does not contains the variable references

{
    books(author: null) {
        id
        name
        authors {
            name
        }
    }
    authors {
        name
    }
}