This is a regression due to the changes for
KAFKA-8523. KAFKA-8523 was backported to multiple versions, and was released into 2.2.2, 2.3.1, and 2.4.0, and will soon be released in 2.5.0.
Unfortunately, that fix always makes the `InsertField` SMT skip all tombstone records, even when using the `InsertField$Key`.
the correct behavior would be:
The method no longer detects just tombstone methods, so the code should be refactored to return the record if the operatingValue for the record (which for `InsertField$Key` is the record key and for `InsertField$Value` is the record value) is null.