[ 
https://issues.apache.org/jira/browse/SPARK-21677?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16121641#comment-16121641
 ] 

Jen-Ming Chung commented on SPARK-21677:
----------------------------------------

to [~hyukjin.kwon], the return {{NULL}} you mentioned does it means all fields 
should be null in json_tuple, or just the non-existence field as shown in the 
following. Thanks!

{code:language=scala|borderStyle=solid}
e.g., spark.sql("""SELECT json_tuple('{"a":1, "b":2}', 'a', 'b', 
'not_exising_fields')""").show()

+---+---+----+
| c0| c1|  c2|
+---+---+----+
|  1|  2|null|
+---+---+----+
{code}



> json_tuple throws NullPointException when column is null as string type.
> ------------------------------------------------------------------------
>
>                 Key: SPARK-21677
>                 URL: https://issues.apache.org/jira/browse/SPARK-21677
>             Project: Spark
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 2.3.0
>            Reporter: Hyukjin Kwon
>            Priority: Minor
>              Labels: Starter
>
> I was testing {{json_tuple}} before using this to extract values from JSONs 
> in my testing cluster but I found it could actually throw  
> {{NullPointException}} as below sometimes:
> {code}
> scala> Seq(("""{"Hyukjin": 224, "John": 
> 1225}""")).toDS.selectExpr("json_tuple(value, trim(' Hyukjin    '))").show()
> +---+
> | c0|
> +---+
> |224|
> +---+
> scala> Seq(("""{"Hyukjin": 224, "John": 
> 1225}""")).toDS.selectExpr("json_tuple(value, trim(' Jackson    '))").show()
> +----+
> |  c0|
> +----+
> |null|
> +----+
> scala> Seq(("""{"Hyukjin": 224, "John": 
> 1225}""")).toDS.selectExpr("json_tuple(value, trim(null))").show()
> ...
> java.lang.NullPointerException
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple$$anonfun$foldableFieldNames$1.apply(jsonExpressions.scala:367)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple$$anonfun$foldableFieldNames$1.apply(jsonExpressions.scala:366)
>       at 
> scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
>       at 
> scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234)
>       at 
> scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
>       at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
>       at scala.collection.TraversableLike$class.map(TraversableLike.scala:234)
>       at scala.collection.AbstractTraversable.map(Traversable.scala:104)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple.foldableFieldNames$lzycompute(jsonExpressions.scala:366)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple.foldableFieldNames(jsonExpressions.scala:365)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple.constantFields$lzycompute(jsonExpressions.scala:373)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple.constantFields(jsonExpressions.scala:373)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple.org$apache$spark$sql$catalyst$expressions$JsonTuple$$parseRow(jsonExpressions.scala:417)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple$$anonfun$eval$4.apply(jsonExpressions.scala:401)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple$$anonfun$eval$4.apply(jsonExpressions.scala:400)
>       at org.apache.spark.util.Utils$.tryWithResource(Utils.scala:2559)
>       at 
> org.apache.spark.sql.catalyst.expressions.JsonTuple.eval(jsonExpressions.scala:400)
> {code}
> It sounds we should show explicit error messages or return {{NULL}}.



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