in src/main/java/org/apache/sling/distribution/journal/kafka/KafkaJsonMessageSender.java [58:62]
public KafkaJsonMessageSender(KafkaProducer<String, String> producer, String topic, ExceptionEventSender eventSender) {
this.topic = topic;
this.eventSender = eventSender;
this.producer = requireNonNull(producer);
}