presto-hive/src/main/java/io/prestosql/plugin/hive/GenericHiveRecordCursor.java/GenericHiveRecordCursor/isNull
class GenericHiveRecordCursor:    @Override
    public boolean isNull(int fieldId)
    {
        checkState(!closed, "Cursor is closed");

        if (!loaded[fieldId]) {
            parseColumn(fieldId);
        }
        return nulls[fieldId];
    }