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 createDecimalMaxPrecision<Decimal256>(scale);
            throw Exception("Unexpected branch in code of conversion function: it is a bug.", ErrorCodes::LOGICAL_ERROR);
        }
        else
        {
            
            UInt8 timezone_arg_position = 1;
            UInt32 scale [[maybe_unused]] = DataTypeDateTime64::default_scale;
            
            if (isDateTime64<Name, ToDataType>(arguments))
            {
                timezone_arg_position += 1;
                scale = static_cast<UInt32>(arguments[1].column->get64(0));
                if (to_datetime64 || scale != 0) 
                    return std::make_shared<DataTypeDateTime64>(scale,
                        extractTimeZoneNameFromFunctionArguments(arguments, timezone_arg_position, 0));
                return std::make_shared<DataTypeDateTime>(extractTimeZoneNameFromFunctionArguments(arguments, timezone_arg_position, 0));
            }
            if constexpr (std::is_same_v<ToDataType, DataTypeDateTime>)
                return std::make_shared<DataTypeDateTime>(extractTimeZoneNameFromFunctionArguments(arguments, timezone_arg_position, 0));
            else if constexpr (std::is_same_v<ToDataType, DataTypeDateTime64>)
                throw Exception("Unexpected branch in code of conversion function: it is a bug.", ErrorCodes::LOGICAL_ERROR);
            else
                return std::make_shared<ToDataType>();
        }
    }
    
    
    
    bool useDefaultImplementationForNulls() const override