**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+
&& right_float <= static_cast<Float64>(std::numeric_limits<T>::max()))
                return { .is_monotonic = true };
            return {};
        }
        
        const bool from_is_unsigned = type.isValueRepresentedByUnsignedInteger();
        const bool to_is_unsigned = is_unsigned_v<T>;
        const size_t size_of_from = type.getSizeOfValueInMemory();
        const size_t size_of_to = sizeof(T);
        const bool left_in_first_half = left.isNull()
            ? from_is_unsigned
            : (left.get<Int64>() >= 0);
        const bool right_in_first_half = right.isNull()
            ? !from_is_unsigned
            : (right.get<Int64>() >= 0);
        
        if (size_of_from == size_of_to)
        {
            if (from_is_unsigned == to_is_unsigned)
                return { .is_monotonic = true, .is_always_monotonic = true };
            if (left_in_first_half == right_in_first_half)
                return { .is_monotonic = true };
            return {};
        }
        
        if (size_of_from < size_of_to)
        {
            if (from_is_unsigned == to_is_unsigned)
                return { .is_monotonic = true, .is_always_monotonic = true };
            if (!to_is_unsigned)