**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<FromDataType, DataTypeFixedString>)
            while (!in.eof() && *in.position() == 0)
                ++in.position();
        if (in.eof())
            return true;
        
        if constexpr (std::is_same_v<ToDataType, DataTypeDate> || std::is_same_v<ToDataType, DataTypeDate32>)
        {
            if (!in.eof() && (*in.position() == ' ' || *in.position() == 'T'))
            {
                if (in.buffer().size() == strlen("YYYY-MM-DD hh:mm:ss"))
                    return true;
                if (in.buffer().size() >= strlen("YYYY-MM-DD hh:mm:ss.x")
                    && in.buffer().begin()[19] == '.')
                {
                    in.position() = in.buffer().begin() + 20;
                    while (!in.eof() && isNumericASCII(*in.position()))
                        ++in.position();
                    if (in.eof())
                        return true;
                }
            }
        }
        return false;
    }
    template <typename Additions = void *>
    static ColumnPtr execute(const ColumnsWithTypeAndName & arguments, const DataTypePtr & res_type, size_t input_rows_count,