@Override
    public void subscribe(Pattern pattern) {
        subscribeInternal(pattern, Optional.empty());
    }
This determines if the {@link #pendingOffsetFetchEvent pending offset fetch event} can be reused. Reuse
is only possible if all the following conditions are true:

<ul>
    <li>A pending offset fetch event exists</li>
    <li>The partition set of the pending offset fetch event is the same as the given partition set</li>
    <li>The pending offset fetch event has not expired</li>
</ul>
clients/src/main/java/org/apache/kafka/clients/consumer/internals/AsyncKafkaConsumer.java