public void add(BackgroundEvent event) {
        Objects.requireNonNull(event, "BackgroundEvent provided to add must be non-null");
        backgroundEventQueue.add(event);
    }
Add a {@link BackgroundEvent} to the handler.

@param event A {@link BackgroundEvent} created by the {@link ConsumerNetworkThread network thread}
clients/src/main/java/org/apache/kafka/clients/consumer/internals/events/BackgroundEventHandler.java