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?
(*vec_null_map_to)[i] = !parsed;
            }
            current_offset = next_offset;
        }
        if constexpr (exception_mode == ConvertFromStringExceptionMode::Null)
            return ColumnNullable::create(std::move(col_to), std::move(col_null_map_to));
        else
            return col_to;
    }
};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeString>)
struct ConvertImpl<DataTypeString, ToDataType, Name, ConvertDefaultBehaviorTag>
    : ConvertThroughParsing<DataTypeString, ToDataType, Name, ConvertFromStringExceptionMode::Throw, ConvertFromStringParsingMode::Normal> {};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeFixedString>)
struct ConvertImpl<DataTypeFixedString, ToDataType, Name, ConvertDefaultBehaviorTag>
    : ConvertThroughParsing<DataTypeFixedString, ToDataType, Name, ConvertFromStringExceptionMode::Throw, ConvertFromStringParsingMode::Normal> {};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeString>)
struct ConvertImpl<DataTypeString, ToDataType, Name, ConvertReturnNullOnErrorTag>
    : ConvertThroughParsing<DataTypeString, ToDataType, Name, ConvertFromStringExceptionMode::Null, ConvertFromStringParsingMode::Normal> {};
template <typename ToDataType, typename Name>
requires (!std::is_same_v<ToDataType, DataTypeFixedString>)
struct ConvertImpl<DataTypeFixedString, ToDataType, Name, ConvertReturnNullOnErrorTag>
    : ConvertThroughParsing<DataTypeFixedString, ToDataType, Name, ConvertFromStringExceptionMode::Null, ConvertFromStringParsingMode::Normal> {};
template <typename StringColumnType>
struct ConvertImplGenericFromString
{
    static ColumnPtr execute(ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, const ColumnNullable *, size_t input_rows_count)