**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+
template <> struct FunctionTo<DataTypeDateTime64> { using Type = FunctionToDateTime64; };
template <> struct FunctionTo<DataTypeUUID> { using Type = FunctionToUUID; };
template <> struct FunctionTo<DataTypeString> { using Type = FunctionToString; };
template <> struct FunctionTo<DataTypeFixedString> { using Type = FunctionToFixedString; };
template <> struct FunctionTo<DataTypeDecimal<Decimal32>> { using Type = FunctionToDecimal32; };
template <> struct FunctionTo<DataTypeDecimal<Decimal64>> { using Type = FunctionToDecimal64; };
template <> struct FunctionTo<DataTypeDecimal<Decimal128>> { using Type = FunctionToDecimal128; };
template <> struct FunctionTo<DataTypeDecimal<Decimal256>> { using Type = FunctionToDecimal256; };
template <typename FieldType> struct FunctionTo<DataTypeEnum<FieldType>>
    : FunctionTo<DataTypeNumber<FieldType>>
{
};
struct NameToUInt8OrZero { static constexpr auto name = "toUInt8OrZero"; };
struct NameToUInt16OrZero { static constexpr auto name = "toUInt16OrZero"; };
struct NameToUInt32OrZero { static constexpr auto name = "toUInt32OrZero"; };
struct NameToUInt64OrZero { static constexpr auto name = "toUInt64OrZero"; };
struct NameToUInt128OrZero { static constexpr auto name = "toUInt128OrZero"; };
struct NameToUInt256OrZero { static constexpr auto name = "toUInt256OrZero"; };
struct NameToInt8OrZero { static constexpr auto name = "toInt8OrZero"; };
struct NameToInt16OrZero { static constexpr auto name = "toInt16OrZero"; };
struct NameToInt32OrZero { static constexpr auto name = "toInt32OrZero"; };
struct NameToInt64OrZero { static constexpr auto name = "toInt64OrZero"; };
struct NameToInt128OrZero { static constexpr auto name = "toInt128OrZero"; };
struct NameToInt256OrZero { static constexpr auto name = "toInt256OrZero"; };
struct NameToFloat32OrZero { static constexpr auto name = "toFloat32OrZero"; };
struct NameToFloat64OrZero { static constexpr auto name = "toFloat64OrZero"; };
struct NameToDateOrZero { static constexpr auto name = "toDateOrZero"; };
struct NameToDate32OrZero { static constexpr auto name = "toDate32OrZero"; };
struct NameToDateTimeOrZero { static constexpr auto name = "toDateTimeOrZero"; };
struct NameToDateTime64OrZero { static constexpr auto name = "toDateTime64OrZero"; };