[SPARK-17773] Input/Output] Add VoidObjectInspector

## What changes were proposed in this pull request?
Added VoidObjectInspector to the list of PrimitiveObjectInspectors

## How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)
Executing following query was failing.
select SOME_UDAF*(a.arr)
from (
select Array(null) as arr from dim_one_row
) a

After the fix, I am getting the correct output:
res0: Array[org.apache.spark.sql.Row] = Array([null])

Author: Ergin Seyfe <eseyfe@fb.com>

Closes #15337 from seyfe/add_void_object_inspector.

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveInspectors.scala

@@ -319,6 +319,8 @@ private[hive] trait HiveInspectors {
         withNullSafe(o => getTimestampWritable(o))
       case _: TimestampObjectInspector =>
         withNullSafe(o => DateTimeUtils.toJavaTimestamp(o.asInstanceOf[Long]))
+      case _: VoidObjectInspector =>
+        (_: Any) => null // always be null for void object inspector
     }
 
     case soi: StandardStructObjectInspector =>

sql/hive/src/test/scala/org/apache/spark/sql/hive/HiveInspectorSuite.scala

@@ -81,6 +81,7 @@ class HiveInspectorSuite extends SparkFunSuite with HiveInspectors {
 
   val data =
     Literal(true) ::
+    Literal(null) ::
     Literal(0.asInstanceOf[Byte]) ::
     Literal(0.asInstanceOf[Short]) ::
     Literal(0) ::