**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+
using FunctionToInt64OrNull = FunctionConvertFromString<DataTypeInt64, NameToInt64OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToInt128OrNull = FunctionConvertFromString<DataTypeInt128, NameToInt128OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToInt256OrNull = FunctionConvertFromString<DataTypeInt256, NameToInt256OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToFloat32OrNull = FunctionConvertFromString<DataTypeFloat32, NameToFloat32OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToFloat64OrNull = FunctionConvertFromString<DataTypeFloat64, NameToFloat64OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDateOrNull = FunctionConvertFromString<DataTypeDate, NameToDateOrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDate32OrNull = FunctionConvertFromString<DataTypeDate32, NameToDate32OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDateTimeOrNull = FunctionConvertFromString<DataTypeDateTime, NameToDateTimeOrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDateTime64OrNull = FunctionConvertFromString<DataTypeDateTime64, NameToDateTime64OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDecimal32OrNull = FunctionConvertFromString<DataTypeDecimal<Decimal32>, NameToDecimal32OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDecimal64OrNull = FunctionConvertFromString<DataTypeDecimal<Decimal64>, NameToDecimal64OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDecimal128OrNull = FunctionConvertFromString<DataTypeDecimal<Decimal128>, NameToDecimal128OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToDecimal256OrNull = FunctionConvertFromString<DataTypeDecimal<Decimal256>, NameToDecimal256OrNull, ConvertFromStringExceptionMode::Null>;
using FunctionToUUIDOrNull = FunctionConvertFromString<DataTypeUUID, NameToUUIDOrNull, ConvertFromStringExceptionMode::Null>;
struct NameParseDateTimeBestEffort { static constexpr auto name = "parseDateTimeBestEffort"; };
struct NameParseDateTimeBestEffortOrZero { static constexpr auto name = "parseDateTimeBestEffortOrZero"; };
struct NameParseDateTimeBestEffortOrNull { static constexpr auto name = "parseDateTimeBestEffortOrNull"; };
struct NameParseDateTimeBestEffortUS { static constexpr auto name = "parseDateTimeBestEffortUS"; };
struct NameParseDateTimeBestEffortUSOrZero { static constexpr auto name = "parseDateTimeBestEffortUSOrZero"; };
struct NameParseDateTimeBestEffortUSOrNull { static constexpr auto name = "parseDateTimeBestEffortUSOrNull"; };
struct NameParseDateTime32BestEffort { static constexpr auto name = "parseDateTime32BestEffort"; };
struct NameParseDateTime32BestEffortOrZero { static constexpr auto name = "parseDateTime32BestEffortOrZero"; };
struct NameParseDateTime32BestEffortOrNull { static constexpr auto name = "parseDateTime32BestEffortOrNull"; };
struct NameParseDateTime64BestEffort { static constexpr auto name = "parseDateTime64BestEffort"; };
struct NameParseDateTime64BestEffortOrZero { static constexpr auto name = "parseDateTime64BestEffortOrZero"; };
struct NameParseDateTime64BestEffortOrNull { static constexpr auto name = "parseDateTime64BestEffortOrNull"; };
struct NameParseDateTime64BestEffortUS { static constexpr auto name = "parseDateTime64BestEffortUS"; };
struct NameParseDateTime64BestEffortUSOrZero { static constexpr auto name = "parseDateTime64BestEffortUSOrZero"; };
struct NameParseDateTime64BestEffortUSOrNull { static constexpr auto name = "parseDateTime64BestEffortUSOrNull"; };
using FunctionParseDateTimeBestEffort = FunctionConvertFromString<