**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+
safe_convert_custom_types = to_type->getCustomName() && from_type_custom_name->getName() == to_type->getCustomName()->getName();
        if (from_type->equals(*to_type) && safe_convert_custom_types)
            return createIdentityWrapper(from_type);
        else if (WhichDataType(from_type).isNothing())
            return createNothingWrapper(to_type.get());
        WrapperType ret;
        auto make_default_wrapper = [&](const auto & types) -> bool
        {
            using Types = std::decay_t<decltype(types)>;
            using ToDataType = typename Types::LeftType;
            if constexpr (
                std::is_same_v<ToDataType, DataTypeUInt16> ||
                std::is_same_v<ToDataType, DataTypeUInt32> ||
                std::is_same_v<ToDataType, DataTypeUInt64> ||
                std::is_same_v<ToDataType, DataTypeUInt128> ||
                std::is_same_v<ToDataType, DataTypeUInt256> ||
                std::is_same_v<ToDataType, DataTypeInt8> ||
                std::is_same_v<ToDataType, DataTypeInt16> ||
                std::is_same_v<ToDataType, DataTypeInt32> ||
                std::is_same_v<ToDataType, DataTypeInt64> ||
                std::is_same_v<ToDataType, DataTypeInt128> ||
                std::is_same_v<ToDataType, DataTypeInt256> ||
                std::is_same_v<ToDataType, DataTypeFloat32> ||
                std::is_same_v<ToDataType, DataTypeFloat64> ||
                std::is_same_v<ToDataType, DataTypeDate> ||
                std::is_same_v<ToDataType, DataTypeDate32> ||
                std::is_same_v<ToDataType, DataTypeDateTime> ||
                std::is_same_v<ToDataType, DataTypeUUID>)
            {
                ret = createWrapper(from_type, checkAndGetDataType<ToDataType>(to_type.get()), requested_result_is_nullable);