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Current state: Under Discussion

Discussion thread:  https://listswww.mail-archive.com/dev@kafka.apache.org/threadmsg105887.html/r69b11ca1d298a5c849f8af1af0b2708abfc5b1c3e44a402917f6646c%40%3Cdev.kafka.apache.org%3E

JIRA: 

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Generally, when an optional field which has default value is null, we can treat it as null or default value, it depends on the context.

Public Interfaces

Add a config

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 property `serialize.accept.optional.

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null`,

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 default

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 `false`, for compatibility.

Proposed Changes

Config property change

Add a config property property `serialize.accept.optional.null null` in org.apache.kafka.connect.storage.ConverterConfig, default false. This property would only affect JsonConverter in all build-in converters , both  serialization and deserialization. Any third party converters can extend ConverterConfig just like JsonConverterConfig to read this property and implement it.

JsonConverter change

Change private fields TO_CONNECT_CONVERTERS, LOGICAL_CONVERTERS, and private method convertToConnect(Schema schema, JsonNode jsonValue) to no-static.

Serialization(convertToJson),

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 for an optional null field which has default value,

• if set serialize.accept.optional.null=true, take null; 

• if

  set accept.optional.null=false, take default value.

Deserialization(convertToConnectData), for an optional null field which has default value,

• if set

   set serialize.accept.optional.null=

  true, take null; if set accept.optional.null=

  false, take default value.

Compatibility, Deprecation, and Migration Plan

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1. Always take null on an optional null field which has default value. It will break the compatibility and only cover partial cases.
2. Apply for both serialization and deserialization. I have not see scenario in deserialization.