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

[Shang Yuanchun (Jira)]

Caizhi Weng created FLINK-17083:
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             Summary: 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


[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 throws a related exception to the users instead of giving the users a somewhat unrelated exception.



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