private void process(final SubscriptionChangeEvent ignored) {
        if (!requestManagers.heartbeatRequestManager.isPresent()) {
            log.warn("Group membership manager not present when processing a subscribe event");
            return;
        }
        MembershipManager membershipManager = requestManagers.heartbeatRequestManager.get().membershipManager();
        membershipManager.onSubscriptionUpdated();
    }
Process event that indicates that the subscription changed. This will make the
consumer join the group if it is not part of it yet, or send the updated subscription if
it is already a member.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/events/ApplicationEventProcessor.java