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https://issues.apache.org/jira/browse/KAFKA-13641?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17486427#comment-17486427
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Mohammad Yousuf Minhaj Zia commented on KAFKA-13641:
----------------------------------------------------
If I am not wrong, the `ValueJoiner` is a java class which is sort of like a
function signature with generic parameters `value1` and `value2`. What I would
like is to create a Scala wrapper such that:
```
type ValueLeftJoiner[A, B, C) => (A, Option[B]) => C
type ValueOuterJoiner[A, B, C) => (Option[A], B) => C
type ValueInnerJoiner[A, B, C) => (A, B) => C
```
or to deal with tombstones just make both inputs optional with a central
ValueJoiner:
```
type ValueJoiner[A, B, C) => (Option[A], Option[B]) => C
```
Unfortunately this makes things quite inconsistent with the rest of the
codebase because a null could be returned or be a parameter virtually anywhere
apart from joiners.
Wondering if we will ever making the explicitness of nullable fields better in
Kafka?
> Kafka Streams Scala: Add `Option` to `ValueJoiner` parameters
> -------------------------------------------------------------
>
> Key: KAFKA-13641
> URL: https://issues.apache.org/jira/browse/KAFKA-13641
> Project: Kafka
> Issue Type: Improvement
> Components: streams
> Reporter: Mohammad Yousuf Minhaj Zia
> Priority: Minor
>
> Since `ValueJoiner` right parameter in `leftJoins`, `outerJoins` can be
> nullable, I am wondering if can wrap them around Scala `Option`.
> However, there is also the concern that the left hand side value can be null
> in the case of tombstone messages, in which the `Option` semantics can be
> misleading. I still feel this could be a useful feature in reducing the
> number of `NullPointerExceptions`.
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