Elastic 8.1.1 - Cannot instantiate FunctionScore, build() protected

I am trying to migrate some elastic functionalty from elasticsearch 6.5.4 -> 8.1.1, specifically a functionScoreQuery:

private SearchRequest buildRequest(String query) {

    SearchRequest searchRequest = new SearchRequest(INDEX_ALIAS);
    SearchSourceBuilder sourceBuilder = new SearchSourceBuilder();
    sourceBuilder.query(QueryBuilders.functionScoreQuery(
            getQuery(),
            getFilterFunctions())
    );
    searchRequest.source(sourceBuilder);
    return searchRequest;
}

private FilterFunctionBuilder[] getFilterFunctions() {
    return new FilterFunctionBuilder[] {
            boostFunction(termQuery("Term1", "Value1").boost(2.0f)),
            boostFunction(termQuery("Term2", "Value2").boost(1.5f)),
            };
}

private FunctionScoreQueryBuilder.FilterFunctionBuilder boostFunction(QueryBuilder query{
    return new FilterFunctionBuilder(query, weightFactorFunction(1.0f));
}

I cannot figure out how to do this with the new java api. I am trying something like this:

    private SearchRequest buildRequest(String query, int numberOfResults) {
        return new SearchRequest.Builder()
                .index(INDEX_ALIAS)
                .query(buildQuery(query))
                .build();
    }

    private Query buildQuery(String queryWithoutDots) {
        return new Query.Builder()
                .functionScore(f -> f
                        .query(getQueries())
                        .functions(getFilterFunctions())
                )
                .build();
    }

    private List<FunctionScore> getFilterFunctions() {
        return List.of(
               new FunctionScore.Builder()
                    .filter(new Query.Builder()
                            .term(t -> 
                         t.queryName("Term1")
                                    .value("Value1")
                                    .boost(2.0f))
                            .build())
                    **.build(),**
               new FunctionScore.Builder()
                    .filter(new Query.Builder()
                            .term(t -> 
                                    t.queryName("Term2")
                                    .value("Value2")
                                    .boost(1.5f))
                            .build())
                    **.build(),**
    }

But it is not possible to instantiate a FunctionScore as

'build()' has protected access in 'co.elastic.clients.elasticsearch._types.query_dsl.FunctionScore

Is this a bug? Is there any other approach i should consider?

I figured it out. I need to use a modifier for instance: linear

new FunctionScore.Builder()
    .linear(
        l -> l.filter(
            f -> f.term(
                t -> t.queryName("Term1")
                      .value("Value1")
                      .boost(2.0f)
            )
        )
    )
 .build()