**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+
to_reverse_index.reserve(to_element_types.size());
            for (size_t i = 0; i < to_element_types.size(); ++i)
                to_reverse_index.emplace_back(i);
        }
        return [element_wrappers, from_element_types, to_element_types, to_reverse_index]
            (ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t input_rows_count) -> ColumnPtr
        {
            const auto * col = arguments.front().column.get();
            size_t tuple_size = to_element_types.size();
            const ColumnTuple & column_tuple = typeid_cast<const ColumnTuple &>(*col);
            Columns converted_columns(tuple_size);
            
            for (size_t i = 0; i < tuple_size; ++i)
            {
                if (to_reverse_index[i])
                {
                    size_t from_idx = *to_reverse_index[i];
                    ColumnsWithTypeAndName element = {{column_tuple.getColumns()[from_idx], from_element_types[from_idx], "" }};
                    converted_columns[i] = element_wrappers[i](element, to_element_types[i], nullable_source, input_rows_count);
                }
                else
                {
                    converted_columns[i] = to_element_types[i]->createColumn()->cloneResized(input_rows_count);
                }
            }
            return ColumnTuple::create(converted_columns);
        };
    }
    
    WrapperType createTupleToMapWrapper(const DataTypes & from_kv_types, const DataTypes & to_kv_types) const