...

ConsoleProducer will be updated to accept a new property: null.marker. By default, it will not be set to keep the existing behavior. When set, if it's equal to the value enteredany of the fields (key, value or headers) in the input match the marker, a record with the value that field set to null will be produced.

Example:

$ ./bin/kafka-console-producer.sh --bootstrap-server localhost:290929092 --topic test --property null.marker=NULL
>NULL               (1)
>NULL more content  (2)

1. This will result in a record with value=null.
2. The record will have its value set to "NULL more content". The value has to exactly match the marker to be replaced by null.
   

Example with key and headers:

$ ./bin/kafka-console-producer.sh --bootstrap-server localhost:9092 --topic test --property null.marker=NULL --property parse.key=true --property parse.headers=true
>h0:v0,h1:v1 NULL myvalue   (1)
>NULL mykey NULL            (2)
>h0:,h1:v1 NULL NULL        (3)
>h0:NULL,h1:v1 mykey NULL   (4)

1. This will result in a record with key=null, value="myvalue" and headers={"h0": "v0", "h1": "v1"}
2. This will result in a record with key="mykey", value=null and headers=null
3. This will result in a record with key=null, value=null and headers={"h0": "", "h1": "v1"}
4. This will result in a record with key="mykey", value=null and headers={"h0": null, "h1": "v1"}

Proposed Changes

This will require small changes in ConsoleProducer/LineMessageReader to accept the new flag and update the generated ProducerRecord accordingly.

...