**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+
{
        auto getter = [&] (const auto & args) { return getReturnTypeImplRemovedNullable(args); };
        auto res = getReturnTypeDefaultImplementationForNulls(arguments, getter);
        to_nullable = res->isNullable();
        checked_return_type = true;
        return res;
    }
    DataTypePtr getReturnTypeImplRemovedNullable(const ColumnsWithTypeAndName & arguments) const
    {
        FunctionArgumentDescriptors mandatory_args = {{"Value", nullptr, nullptr, nullptr}};
        FunctionArgumentDescriptors optional_args;
        if constexpr (to_decimal)
        {
            mandatory_args.push_back({"scale", &isNativeInteger<IDataType>, &isColumnConst, "const Integer"});
        }
        if (!to_decimal && isDateTime64<Name, ToDataType>(arguments))
        {
            mandatory_args.push_back({"scale", &isNativeInteger<IDataType>, &isColumnConst, "const Integer"});
        }