**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+
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 (left.isNull() || right.isNull())
                return {};
            
            if (divideByRangeOfType(left.get<UInt64>()) != divideByRangeOfType(right.get<UInt64>()))
                return {};
            if (to_is_unsigned)
                return { .is_monotonic = true };
            else
            {
                
                const bool is_monotonic = (T(left.get<UInt64>()) >= 0) == (T(right.get<UInt64>()) >= 0);
                return { .is_monotonic = is_monotonic };
            }
        }
        __builtin_unreachable();
    }
};
struct ToDateMonotonicity
{
    static bool has() { return true; }