**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+
size_t size = col_from->size();
            size_t n = col_from->getN();
            data_to.resize(size * (n + 1)); 
            offsets_to.resize(size);
            size_t offset_from = 0;
            size_t offset_to = 0;
            for (size_t i = 0; i < size; ++i)
            {
                size_t bytes_to_copy = n;
                while (bytes_to_copy > 0 && data_from[offset_from + bytes_to_copy - 1] == 0)
                    --bytes_to_copy;
                memcpy(&data_to[offset_to], &data_from[offset_from], bytes_to_copy);
                offset_from += n;
                offset_to += bytes_to_copy;
                data_to[offset_to] = 0;
                ++offset_to;
                offsets_to[i] = offset_to;
            }
            data_to.resize(offset_to);
            return col_to;
        }
        else
            throw Exception("Illegal column " + arguments[0].column->getName()
                    + " of first argument of function " + Name::name,
                ErrorCodes::ILLEGAL_COLUMN);
    }
};
struct NameToDate { static constexpr auto name = "toDate"; };
struct NameToDate32 { static constexpr auto name = "toDate32"; };
struct NameToDateTime { static constexpr auto name = "toDateTime"; };