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https://issues.apache.org/jira/browse/HIVE-6922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13973738#comment-13973738
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Xuefu Zhang commented on HIVE-6922:
-----------------------------------
Sounds good then. Thanks for the explanation.
> NullPointerException in collect_set() UDAF
> ------------------------------------------
>
> Key: HIVE-6922
> URL: https://issues.apache.org/jira/browse/HIVE-6922
> Project: Hive
> Issue Type: Bug
> Components: UDF
> Reporter: Sun Rui
> Assignee: Sun Rui
> Attachments: HIVE-6922.patch
>
>
> Steps to reproduce the bug:
> {noformat}
> create table temp(key int, value string);
> -- leave the table empty
> select collect_set(key) from temp where key=0;
> Error: java.lang.RuntimeException: Hive Runtime Error while closing
> operators: java.lang.NullPointerException
> at
> org.apache.hadoop.hive.ql.exec.mr.ExecReducer.close(ExecReducer.java:326)
> at
> org.apache.hadoop.mapred.ReduceTask.runOldReducer(ReduceTask.java:471)
> at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:408)
> at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:162)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:396)
> at
> org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1477)
> at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:157)
> Caused by: org.apache.hadoop.hive.ql.metadata.HiveException:
> java.lang.NullPointerException
> at
> org.apache.hadoop.hive.ql.exec.GroupByOperator.closeOp(GroupByOperator.java:1141)
> at org.apache.hadoop.hive.ql.exec.Operator.close(Operator.java:577)
> at
> org.apache.hadoop.hive.ql.exec.mr.ExecReducer.close(ExecReducer.java:318)
> ... 7 more
> Caused by: java.lang.NullPointerException
> at
> org.apache.hadoop.hive.ql.udf.generic.GenericUDAFMkCollectionEvaluator.merge(GenericUDAFMkCollectionEvaluator.java:140)
> at
> org.apache.hadoop.hive.ql.udf.generic.GenericUDAFEvaluator.aggregate(GenericUDAFEvaluator.java:186)
> at
> org.apache.hadoop.hive.ql.exec.GroupByOperator.closeOp(GroupByOperator.java:1132)
> ... 9 more
> {noformat}
> The root cause is that in GenericUDAFMkCollectionEvaluator.merge()
> partialResult could be null but is not validated before it is used.
> {code}
> List<Object> partialResult = (ArrayList<Object>)
> internalMergeOI.getList(partial);
> for(Object i : partialResult) {
> putIntoCollection(i, myagg);
> }
> {code}
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