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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