[jira] [Commented] (FLINK-17083) Restrict users of accumulators not to return null in Accumulator#getLocalValue

["Aljoscha Krettek (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-17083?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17083040#comment-17083040 ] 

Aljoscha Krettek commented on FLINK-17083:
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Yes, I think that restriction makes sense.

> Restrict users of accumulators not to return null in Accumulator#getLocalValue
> ------------------------------------------------------------------------------
>
>                 Key: FLINK-17083
>                 URL: https://issues.apache.org/jira/browse/FLINK-17083
>             Project: Flink
>          Issue Type: Improvement
>          Components: API / Core
>    Affects Versions: 1.11.0
>            Reporter: Caizhi Weng
>            Priority: Major
>
> [This discussion|https://issues.apache.org/jira/browse/FLINK-13880] raises a problem that, if a user returns a null value in {{Accumulator#getLocalValue}}, he will be notified that the {{failureCause}} should not be null when fetching the accumulator result, which seems to be really wired.
> The problem is that we're not explicitly restricting the users not to return null values in {{Accumulator#getLocalValue}}.
> [~aljoscha] is it legal to return null values? If not, we should explicitly throw a related exception to the users instead of giving the users a somewhat unrelated exception.



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