**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+
const auto nested_function = prepareUnpackDictionaries(from_nested_type, to_nested_type);
        return [nested_function, from_nested_type, to_nested_type](
                ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t ) -> ColumnPtr
        {
            const auto & argument_column = arguments.front();
            const ColumnArray * col_array = nullptr;
            if (const ColumnMap * col_map = checkAndGetColumn<ColumnMap>(argument_column.column.get()))
                col_array = &col_map->getNestedColumn();
            else
                col_array = checkAndGetColumn<ColumnArray>(argument_column.column.get());
            if (col_array)
            {
                
                ColumnsWithTypeAndName nested_columns{{ col_array->getDataPtr(), from_nested_type, "" }};
                
                auto result_column = nested_function(nested_columns, to_nested_type, nullable_source, nested_columns.front().column->size());
                
                return ColumnArray::create(result_column, col_array->getOffsetsPtr());
            }
            else
            {
                throw Exception(ErrorCodes::LOGICAL_ERROR,
                    "Illegal column {} for function CAST AS Array",
                    argument_column.column->getName());
            }
        };
    }
    using ElementWrappers = std::vector<WrapperType>;
    ElementWrappers getElementWrappers(const DataTypes & from_element_types, const DataTypes & to_element_types) const