Fix to Delta Uniform to support convert Delta null partition values t…

…o iceberg

The existing Delta to iceberg conversion has a bug that it does not handle null partition values as it will write the string with content "null" in the partition path, and "null" cannot be converted to other numeric types. The fix uses a special marker from iceberg library so it recognizes the null value and converts correctly.

GitOrigin-RevId: 667e795ead753803565340abcc23ae01d9738a2c

iceberg/src/main/scala/org/apache/spark/sql/delta/icebergShaded/IcebergTransactionUtils.scala

@@ -150,6 +150,7 @@ object IcebergTransactionUtils
       .withFormat(FileFormat.PARQUET)
 
     if (partitionSpec.isPartitioned) {
+      val ICEBERG_NULL_PARTITION_VALUE = "__HIVE_DEFAULT_PARTITION__"
       val partitionPath = partitionSpec
         .fields()
         .asScala
@@ -158,7 +159,11 @@ object IcebergTransactionUtils
           // The Iceberg Schema and PartitionSpec all use the column logical names.
           // Delta FileAction::partitionValues, however, uses physical names.
           val physicalPartKey = logicalToPhysicalPartitionNames(logicalPartCol)
-          s"$logicalPartCol=${f.partitionValues(physicalPartKey)}"
+
+          // ICEBERG_NULL_PARTITION_VALUE is referred in Iceberg lib to mark NULL partition value
+          val partValue = Option(f.partitionValues(physicalPartKey))
+            .getOrElse(ICEBERG_NULL_PARTITION_VALUE)
+          s"$logicalPartCol=$partValue"
         }
         .mkString("/")