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?
-> ColumnPtr
                        {
                            if (!WhichDataType(result_type).isFixedString())
                                throw Exception(
                                    ErrorCodes::TYPE_MISMATCH, "Wrong result type {}. Expected FixedString", result_type->getName());
                            if (cast_ipv4_ipv6_default_on_conversion_error_value)
                                return convertToIPv6<IPStringToNumExceptionMode::Default>(arguments[0].column);
                            else
                                return convertToIPv6<IPStringToNumExceptionMode::Throw>(arguments[0].column);
                        };
                        return true;
                    }
                    ret = &ConvertImplGenericFromString<typename FromDataType::ColumnType>::execute;
                    return true;
                }
            }
            if constexpr (WhichDataType(ToDataType::type_id).isStringOrFixedString())
            {
                if (from_type->getCustomSerialization())
                {
                    ret = [](ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, const ColumnNullable *, size_t input_rows_count) -> ColumnPtr
                    {
                        return ConvertImplGenericToString<typename ToDataType::ColumnType>::execute(arguments, result_type, input_rows_count);
                    };
                    return true;
                }
            }
            return false;
        };
        if (callOnTwoTypeIndexes(from_type->getTypeId(), to_type->getTypeId(), make_custom_serialization_wrapper))