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https://issues.apache.org/jira/browse/FLINK-5335?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15748451#comment-15748451
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ASF GitHub Bot commented on FLINK-5335:
---------------------------------------
Github user StefanRRichter commented on a diff in the pull request:
https://github.com/apache/flink/pull/3005#discussion_r92402545
--- Diff:
flink-streaming-java/src/main/java/org/apache/flink/streaming/api/checkpoint/ListCheckpointed.java
---
@@ -41,6 +41,7 @@
* @param checkpointId The ID of the checkpoint.
* @param timestamp Timestamp of the checkpoint.
* @return The operator state in a list of redistributable, atomic
sub-states.
+ * Should not return null, but empty list instead.
--- End diff --
That is why I wrote "should". It is possible, but not encouraged because i)
`null` is evil ;-) and ii) user will also receive empty list on restore.
> Allow ListCheckpointed user functions to return null
> ----------------------------------------------------
>
> Key: FLINK-5335
> URL: https://issues.apache.org/jira/browse/FLINK-5335
> Project: Flink
> Issue Type: Improvement
> Components: State Backends, Checkpointing
> Reporter: Stefan Richter
> Assignee: Stefan Richter
>
> Currently, it is not allowed to return null as result for the methods in
> {{ListCheckpointed}}. From a usability perspective, I think it is nicer to
> allow this.
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