**Describe what's wrong**

```sql
SELECT toTypeName(s), toString(s) FROM
(
 SELECT toFixedString('',32) AS s 
 UNION ALL
 SELECT null AS s 
)
```

this query works in all versions from 19.17 to 21.8, but stop works after 21.9+ 

https://fiddle.clickhouse.com/7bd65b36-a6e6-470a-8bdc-4c98a33ff453
21.8 works

https://fiddle.clickhouse.com/9e40a424-4027-4c7f-bd41-b20935ae9129
21.9 doesn't work
```
Received exception from server (version 21.9.6):
Code: 44. DB::Exception: Received from localhost:9000. DB::Exception: Illegal column Nullable(FixedString(32)) of first argument of function toString. (ILLEGAL_COLUMN)
```

this query works in all versions

```sql
SELECT toTypeName(s), toString(s) FROM
(
 SELECT '' AS s 
 UNION ALL
 SELECT null AS s 
)
```
https://fiddle.clickhouse.com/4f810f03-1644-4eb7-b696-0341b1bbdbc4


**Does it reproduce on recent release?**
Yes, reproduce in all releases 21.9+
return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeInt128>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeInt256>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeFloat32>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeFloat64>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeDate>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeDate32>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeDateTime>(to_type))
            return monotonicityForType(type);
        if (const auto * type = checkAndGetDataType<DataTypeString>(to_type))
            return monotonicityForType(type);
        if (isEnum(from_type))
        {
            if (const auto * type = checkAndGetDataType<DataTypeEnum8>(to_type))
                return monotonicityForType(type);
            if (const auto * type = checkAndGetDataType<DataTypeEnum16>(to_type))
                return monotonicityForType(type);
        }
        
        return {};
    }
};
}