array_insert: return null when pos is null

Author: cfmcgrady

native/spark-expr/src/array_funcs/array_insert.rs

@@ -222,6 +222,13 @@ fn array_insert<O: OffsetSizeTrait>(
         let start = window[0].as_usize();
         let end = window[1].as_usize();
         let len = end - start;
+
+        // Return null for the entire row when pos is null (consistent with Spark's behavior)
+        if pos_data.is_null(row_index) {
+            new_offsets.push(new_offsets[row_index]);
+            list_valid.push(false);
+            continue;
+        }
         let pos = pos_data.value(row_index);
 
         if list_array.is_null(row_index) {

spark/src/test/scala/org/apache/comet/CometArrayExpressionSuite.scala

@@ -211,11 +211,13 @@ class CometArrayExpressionSuite extends CometTestBase with AdaptiveSparkPlanHelp
             .withColumn("arrInsertResult", expr("array_insert(arr, 1, 1)"))
             .withColumn("arrInsertNegativeIndexResult", expr("array_insert(arr, -1, 1)"))
             .withColumn("arrPosGreaterThanSize", expr("array_insert(arr, 8, 1)"))
+            .withColumn("arrPosIsNull", expr("array_insert(arr, cast(null as int), 1)"))
             .withColumn("arrNegPosGreaterThanSize", expr("array_insert(arr, -8, 1)"))
             .withColumn("arrInsertNone", expr("array_insert(arr, 1, null)"))
           checkSparkAnswerAndOperator(df.select("arrInsertResult"))
           checkSparkAnswerAndOperator(df.select("arrInsertNegativeIndexResult"))
           checkSparkAnswerAndOperator(df.select("arrPosGreaterThanSize"))
+          checkSparkAnswerAndOperator(df.select("arrPosIsNull"))
           checkSparkAnswerAndOperator(df.select("arrNegPosGreaterThanSize"))
           checkSparkAnswerAndOperator(df.select("arrInsertNone"))
         })