I expect it should work:
```
:) select CAST(CAST('{"x" : 1}', 'Object(\'json\')'), 'Object(Nullable(\'json\'))')

SELECT CAST(CAST('{"x" : 1}', 'Object(\'json\')'), 'Object(Nullable(\'json\'))')

Query id: fb057b45-b72a-4d22-9b38-a3136cdf2465


0 rows in set. Elapsed: 0.002 sec.

Received exception from server (version 22.5.1):
Code: 53. DB::Exception: Received from localhost:9000. DB::Exception: Cast to Object can be performed only from flatten named Tuple, Map or String. Got: Object('json'): While processing CAST(CAST('{"x" : 1}', 'Object(\'json\')'), 'Object(Nullable(\'json\'))'). (TYPE_MISMATCH)
```

@CurtizJ what do you think?
{
        return [element_wrappers = getElementWrappers(from_kv_types, to_kv_types), from_kv_types, to_kv_types]
            (ColumnsWithTypeAndName & arguments, const DataTypePtr &, const ColumnNullable * nullable_source, size_t ) -> ColumnPtr
        {
            const auto * col = arguments.front().column.get();
            const auto & column_array = typeid_cast<const ColumnArray &>(*col);
            const auto & nested_data = typeid_cast<const ColumnTuple &>(column_array.getData());
            Columns converted_columns(2);
            for (size_t i = 0; i < 2; ++i)
            {
                ColumnsWithTypeAndName element = {{nested_data.getColumnPtr(i), from_kv_types[i], ""}};
                converted_columns[i] = element_wrappers[i](element, to_kv_types[i], nullable_source, (element[0].column)->size());
            }
            return ColumnMap::create(converted_columns[0], converted_columns[1], column_array.getOffsetsPtr());
        };
    }
    WrapperType createMapWrapper(const DataTypePtr & from_type_untyped, const DataTypeMap * to_type) const