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?
{
        const IDataType * from_type = arguments[0].type.get();
        if (checkAndGetDataType<DataTypeString>(from_type))
        {
            return ConvertThroughParsing<DataTypeString, ConvertToDataType, Name, exception_mode, parsing_mode>::execute(
                arguments, result_type, input_rows_count, scale);
        }
        else if (checkAndGetDataType<DataTypeFixedString>(from_type))
        {
            return ConvertThroughParsing<DataTypeFixedString, ConvertToDataType, Name, exception_mode, parsing_mode>::execute(
                arguments, result_type, input_rows_count, scale);
        }
        return nullptr;
    }
    ColumnPtr executeImpl(const ColumnsWithTypeAndName & arguments, const DataTypePtr & result_type, size_t input_rows_count) const override