private void process(final ConsumerRebalanceListenerCallbackCompletedEvent event) {
        if (!requestManagers.heartbeatRequestManager.isPresent()) {
            log.warn(
                "An internal error occurred; the group membership manager was not present, so the notification of the {} callback execution could not be sent",
                event.methodName()
            );
            return;
        }
        MembershipManager manager = requestManagers.heartbeatRequestManager.get().membershipManager();
        manager.consumerRebalanceListenerCallbackCompleted(event);
    }
Process event indicating that the consumer unsubscribed from all topics. This will make
the consumer release its assignment and send a request to leave the group.

@param event Unsubscribe event containing a future that will complete when the callback
             execution for releasing the assignment completes, and the request to leave
             the group is sent out.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/events/ApplicationEventProcessor.java