private void process(final ValidatePositionsEvent event) {
        CompletableFuture<Void> future = requestManagers.offsetsRequestManager.validatePositionsIfNeeded();
        future.whenComplete(complete(event.future()));
    }
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