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https://issues.apache.org/jira/browse/FLINK-5717?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15855926#comment-15855926
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Oriol Orellana commented on FLINK-5717:
---------------------------------------
[~aljoscha] Should I fix it and create a PR to master?
> NPE on SessionWindows with ContinuousProcessingTimeTrigger
> ----------------------------------------------------------
>
> Key: FLINK-5717
> URL: https://issues.apache.org/jira/browse/FLINK-5717
> Project: Flink
> Issue Type: Bug
> Components: DataStream API
> Affects Versions: 1.2.0, 1.1.4
> Reporter: Oriol Orellana
>
> The same bug as https://issues.apache.org/jira/browse/FLINK-4862, but for
> ContinuousProcessingTimeTrigger. I copied the description from that same
> issue.
> *what's the error?*
> The following NPE error is thrown when SessionWindows with
> ContinuousProcessingTimeTrigger is used.
> {code:borderStyle=solid}
> Caused by: java.lang.NullPointerException
> at
> org.apache.flink.streaming.api.windowing.triggers.ContinuousProcessingTimeTrigger.clear(ContinuousProcessingTimeTrigger.java:91)
> at
> org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$Context.clear(WindowOperator.java:768)
> at
> org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$2.merge(WindowOperator.java:310)
> at
> org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$2.merge(WindowOperator.java:297)
> at
> org.apache.flink.streaming.runtime.operators.windowing.MergingWindowSet.addWindow(MergingWindowSet.java:196)
> at
> org.apache.flink.streaming.runtime.operators.windowing.WindowOperator.processElement(WindowOperator.java:297)
> at
> org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:183)
> at
> org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:66)
> at
> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:271)
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:609)
> at java.lang.Thread.run(Thread.java:745)
> {code}
> *how to reproduce ?*
> use ContinuousProcessingTimeTrigger instead of the default EventTimeTrigger
> in SessionWindowing example.
> *what's the cause ?*
> When two session windows are being merged, the states of the two
> ContinuousProcessingTimeTrigger are merged as well and the new namespace is
> the merged window. Later when the context tries to delete Timer from the old
> trigger and looks up the timestamp by the old namespace, null value is
> returned.
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