**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+
}
            }
            if constexpr (std::is_same_v<Additions, AccurateOrNullConvertStrategyAdditions>)
                return ColumnNullable::create(std::move(col_to), std::move(col_null_map_to));
            else
                return col_to;
        }
        else
            throw Exception("Illegal column " + named_from.column->getName() + " of first argument of function " + Name::name,
                ErrorCodes::ILLEGAL_COLUMN);
    }
};
/** Conversion of Date32 to Date: check bounds.
  */
template <typename Name> struct ConvertImpl<DataTypeDate32, DataTypeDate, Name, ConvertDefaultBehaviorTag>
    : DateTimeTransformImpl<DataTypeDate32, DataTypeDate, ToDateImpl> {};
/** Conversion of DateTime to Date: throw off time component.
  */
template <typename Name> struct ConvertImpl<DataTypeDateTime, DataTypeDate, Name, ConvertDefaultBehaviorTag>
    : DateTimeTransformImpl<DataTypeDateTime, DataTypeDate, ToDateImpl> {};
/** Conversion of DateTime to Date32: throw off time component.
  */
template <typename Name> struct ConvertImpl<DataTypeDateTime, DataTypeDate32, Name, ConvertDefaultBehaviorTag>
    : DateTimeTransformImpl<DataTypeDateTime, DataTypeDate32, ToDate32Impl> {};
/** Conversion of Date to DateTime: adding 00:00:00 time component.
  */
struct ToDateTimeImpl
{
    static constexpr auto name = "toDateTime";
    static inline UInt32 execute(UInt16 d, const DateLUTImpl & time_zone)