Converting an column containing an array into json throws an exception

[Feng-Jiang28]

Converting an colunn containing an array into json format throws an exception.

Reproduce:

CPU:

scala> val df = Seq(Array(1, 2, 3)).toDF("a")
scala> df.write.mode("OVERWRITE").parquet("TEMP")
scala> val df2 = spark.read.parquet("TEMP")
scala> df2.select(to_json($"a")).show()
+----------+                                                                    
|to_json(a)|
+----------+
|   [1,2,3]|
+----------+

GPU:

$ $SPARK_HOME/bin/spark-shell --master local[*] --jars ${SPARK_RAPIDS_PLUGIN_JAR} 
--conf spark.plugins=com.nvidia.spark.SQLPlugin 
--conf spark.rapids.sql.enabled=true 
--conf spark.rapids.sql.explain=ALL --driver-java-options '-ea -Duser.timezone=UTC ' 
--conf spark.rapids.sql.expression.JsonTuple=true 
--conf spark.rapids.sql.expression.GetJsonObject=true 
--conf spark.rapids.sql.expression.JsonToStructs=true 
--conf spark.rapids.sql.expression.StructsToJson=true

scala> val df = Seq(Array(1, 2, 3)).toDF("a")
scala> df.write.mode("OVERWRITE").parquet("TEMP")
scala> val df2 = spark.read.parquet("TEMP")
scala> df2.select(to_json($"a")).show()
24/05/25 05:34:56 WARN GpuOverrides: 
!Exec <CollectLimitExec> cannot run on GPU because the Exec CollectLimitExec has been disabled, and is disabled by default because Collect Limit replacement can be slower on the GPU, if huge number of rows in a batch it could help by limiting the number of rows transferred from GPU to CPU. Set spark.rapids.sql.exec.CollectLimitExec to true if you wish to enable it
  @Partitioning <SinglePartition$> could run on GPU
  *Exec <ProjectExec> will run on GPU
    *Expression <Alias> to_json(a#41, Some(UTC)) AS to_json(a)#47 will run on GPU
      *Expression <StructsToJson> to_json(a#41, Some(UTC)) will run on GPU
    *Exec <FileSourceScanExec> will run on GPU

24/05/25 05:34:56 ERROR Executor: Exception in task 0.0 in stage 11.0 (TID 11)
java.lang.ClassCastException: org.apache.spark.sql.types.ArrayType cannot be cast to org.apache.spark.sql.types.StructType
	at org.apache.spark.sql.rapids.GpuStructsToJson.doColumnar(GpuStructsToJson.scala:86)
	at com.nvidia.spark.rapids.GpuUnaryExpression.doItColumnar(GpuExpressions.scala:250)
	at com.nvidia.spark.rapids.GpuUnaryExpression.$anonfun$columnarEval$1(GpuExpressions.scala:261)
	at com.nvidia.spark.rapids.Arm$.withResource(Arm.scala:30)
	at com.nvidia.spark.rapids.GpuUnaryExpression.columnarEval(GpuExpressions.scala:260)
	at com.nvidia.spark.rapids.RapidsPluginImplicits$ReallyAGpuExpression.columnarEval(implicits.scala:35)
	at com.nvidia.spark.rapids.GpuAlias.columnarEval(namedExpressions.scala:110)
	at com.nvidia.spark.rapids.RapidsPluginImplicits$ReallyAGpuExpression.columnarEval(implicits.scala:35)
	at com.nvidia.spark.rapids.GpuProjectExec$.$anonfun$project$1(basicPhysicalOperators.scala:110)
	at com.nvidia.spark.rapids.RapidsPluginImplicits$MapsSafely.$anonfun$safeMap$1(implicits.scala:221)
	at com.nvidia.spark.rapids.RapidsPluginImplicits$MapsSafely.$anonfun$safeMap$1$adapted(implicits.scala:218)
	at scala.collection.immutable.List.foreach(List.scala:431)
	at com.nvidia.spark.rapids.RapidsPluginImplicits$MapsSafely.safeMap(impli