public Set<String> subscription() {
        return delegate.subscription();
    }
Get the current subscription. Will return the same topics used in the most recent call to
{@link #subscribe(Collection, ConsumerRebalanceListener)}, or an empty set if no such call has been made.
@return The set of topics currently subscribed to
clients/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumer.java