The following sql and when the dictionary column contains functions related to null, the results will be incorrect.
```
select * from ( select IF(o_orderpriority IS NULL, 'null', o_orderpriority) AS o_orderpriority from test_string_dict_filter_orc ) as A where o_orderpriority = 'null';
```
```
select * from ( select IFNULL(o_orderpriority, 'null') AS o_orderpriority from test_string_dict_filter_parquet ) as A where o_orderpriority = 'null'
```
```
select * from ( select COALESCE(o_orderpriority, 'null') AS o_orderpriority from test_string_dict_filter_parquet ) as A where o_orderpriority = 'null';
```
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