KIP-289 — Improve the default group id behavior in KafkaConsumer

Accepted Kafka 2.2 Consumer

Changes `KafkaConsumer` behavior so that using the default empty `group.id` raises a clear `InvalidGroupIdException` at construction time when subscribe-based APIs are used, rather than at the first `poll()` call with a confusing error. The inconsistency between `subscribe` (which fails at poll) and `assign` (which works fine without a group.id) causes unexpected runtime failures for users who omit `group.id`.

Protocol Impact

JoinGroup

Details