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https://issues.apache.org/jira/browse/FLINK-10374?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16622213#comment-16622213
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Stefan Richter commented on FLINK-10374:
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Thanks for creating a Jira to track this! +1
> [Map State] Let user value serializer handle null values
> --------------------------------------------------------
>
> Key: FLINK-10374
> URL: https://issues.apache.org/jira/browse/FLINK-10374
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Reporter: Andrey Zagrebin
> Priority: Major
> Fix For: 2.0.0
>
>
> Prior to Flink 2.0, value serializer in map state does not rely on user
> serializer to handle null value. Map serializer always prepends the
> serialized value with one byte boolean flag which signals whether it is null
> or not.
> Map state state supports storing null user values for the following
> get/contains semantics:
> remove(k); contains(k) -> false; put(k, null); get(k) -> null; contains(k) ->
> true;
> It means that if user does not need this semantics and storing null values or
> the user value serializer already supports null values, one byte will be
> always wasted in the serialized value.
> Rather than to hardcode null handling in map state serializer, it can be
> optional and up to the user decide the behaviour. If users want to add null
> support for their serializer, they could wrap it e.g. with NullableSerializer
> which can do the same prepending with null flag.
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