private boolean columnVectorsDifferNullForSameIndex(ColumnVector cv1, ColumnVector cv2, int index) {
    return (cv1.isNull[index] && !cv2.isNull[index]) || (!cv1.isNull[index] && cv2.isNull[index]);
  }
Get the child ColumnVector of ListColumnVector
ql/src/java/org/apache/hadoop/hive/ql/io/parquet/vector/VectorizedListColumnReader.java