Kafka Batch Sink Plugin fails when using the Message Key field variable. Plugin fails to send the message and execution finishes with fail status.

Use case: The pipeline fails with a NullPointerException when the message key field is specified and one of the message is missing a key or key is null for that message.
If the same pipeline is run without specifying the message key field, the pipeline runs successfully.

Expected behaviour: Pipeline should fail with a clear exception message

Proposed fix: Add null check for the key and throw Runtime Exception if message key field value is null in the record.