Hi Kafka community, I’m running MirrorMaker 2 (Kafka Connect, Kafka 4.1.0) and noticed a recurring NullPointerException in MirrorSourceMetrics during high load: exactly here : https://github.com/apache/kafka/blob/61e63f12635ad6ff50c5a4e54d51d725ae82d11a/connect/mirror/src/main/java/org/apache/kafka/connect/mirror/MirrorSourceMetrics.java#L125
java.lang.NullPointerException: Cannot read field "recordAgeSensor" because the return value of "java.util.Map.get(Object)" is null After checking the code, it seems the problem happens when the metrics map doesn’t contain an entry for the partition being processed , a simple NULL check would completely prevent this crash. Looks like this usually occurs when a *rebalance or internal reload* happens while MirrorMaker is under high load. When that happens, the metrics map is refreshed, and the task crashes with this NPE. Kafka Connect treats it as *FATAL*, which *kills the entire task*, and replication for that flow stops until the task is *manually restarted*. The fix looks trivial, that's why I was wondering *why this null check isn’t already in place !!* Maybe I’m missing something, or it’s expected only in specific configurations? Right now, I’ve implemented a local override of the metrics class with a metrics NULL check, and it works fine. I just want to confirm whether this behavior is known or if my MirrorMaker setup could be misconfigured..... *Proposed change:* a null check for the metric to avoid this, or catching the exception . Thanks for any insight on this, Dh.Riadh
