@Override
    public OptionalLong highWatermark() {
        if (isInitialized() && quorum.highWatermark().isPresent()) {
            return OptionalLong.of(quorum.highWatermark().get().offset());
        } else {
            return OptionalLong.empty();
        }
    }
Poll for new events. This allows the client to handle inbound
requests and send any needed outbound requests.
raft/src/main/java/org/apache/kafka/raft/KafkaRaftClient.java