public List<Integer> getCustomSortNullOrder() {
    return customSortNullOrder;
  }
This constructor is used for partitioned CTAS. Basically we pass the name of
partitioned columns, which will all be dynamic partitions since the binding
is done after executing the query in the CTAS.
ql/src/java/org/apache/hadoop/hive/ql/plan/DynamicPartitionCtx.java