twitter/finagle

Hi .. I am new to Finagle and I am using it in my java service. However, I am facing some problem while implementing retries in case of certain HTTP Error codes. The retry policy shouldRetry function does not gets called in case of request failing with certain error codes
here is the snippet of the code i am using to instantiate the client

private Service<Request, Response> buildClient(String host) throws Exception {
    String hostString = String.format("%s:%s", host, "8080");
    PartialFunction<Tuple2<Request, Response>, ResponseClass> typed =
            new AbstractPartialFunction<Tuple2<Request, Response>, ResponseClass>() {
                @Override
                public boolean isDefinedAt(Tuple2<Request, Response> x) {
                    return x._2().status() == Status.InternalServerError() || x._2().status() == Status.ServiceUnavailable();
                    return true;
                }

                @Override
                public ResponseClass apply(Tuple2<Request, Response> x) {
                    return ResponseClass.RetryableFailure();
                }
            };

    return this.hostToClientMap.computeIfAbsent(host, s -> {
        try {
            return ClientBuilder.safeBuild(
                    ClientBuilder.get()
                            .stack(Http.client())
                            .hosts(hostString)
                            .hostConnectionLimit(serviceConfiguration.getHttp_max_conn_per_route())
                            .tcpConnectTimeout(Duration.fromMilliseconds(serviceConfiguration.getHttp_socket_timeout_in_ms()))
                            .keepAlive(true)
                            .tls(LogDispatcherFactory.buildSslContext(serviceConfiguration.getSsm_store_region(),
                                    serviceConfiguration.getPrism_certificate_path(),
                                    serviceConfiguration.getPrism_certificate_key_path(),
                                    serviceConfiguration.getTruststore_password()))
                            .connectTimeout(Duration.fromMilliseconds(serviceConfiguration.getHttp_connect_timeout_in_ms()))
                            .requestTimeout(Duration.fromMilliseconds(serviceConfiguration.getHttp_request_timeout_in_ms()))
                            .retryPolicy(new CustomRetryPolicy())
                            .retryBudget(RetryBudgets.newRetryBudget(Duration.fromSeconds(10), 10, 1))
                            .failFast(false)
                            .responseClassifier(HttpResponseClassifier.apply(typed))
                            .reportTo(DefaultStatsReceiver.get()));
        } catch (Exception e) {
            logger.error(String.format("Error initializing the finagle client for host %s.", hostString), e);
            return null;
        }
    });
}

Any thoughts on this ???