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Hive: NullPointerException in collect_set() UDF

By Dinesh
While using Hive version less than < 0.14. You may get below exception:

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)
It is a bug in Hive where in collect_set() fails if there is no data in table. Refer https://issues.apache.org/jira/browse/HIVE-6922

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