presto-tpcds/src/main/java/io/prestosql/plugin/tpcds/TpcdsRecordSet.java/TpcdsRecordCursor/isNull
class TpcdsRecordCursor:        @Override
        public boolean isNull(int field)
        {
            checkState(row != null, "No current row");
            return row.get(columns.get(field).getPosition()) == null;
        }