I am pulling metric below into Prometheus to get information about messages sent to Kafka brokers. I am seeing that some of them coming without topic. I am wondering what type of messages they are? I would expect only messages sent to specific topic.

kafka_server_brokertopicmetrics_messagesin_total{instance="broker:9999",job="kafka"}
kafka_server_brokertopicmetrics_messagesin_total{instance="broker:9999",job="kafka",topic="TopicEvent"}

Thanks