Failed dumps to json, got invalid type error

[sbant]

I'm using python 3.9

The class:

@dataclass
class TcUiMsg:
    Fairvalue: Optional[dict[str, Fv]] = None

Fv is an object.

use perde.json.dumps to dump

out_txt = perde.json.dumps(msg)

got error:
Exception has occurred: TypeError (note: full exception trace is shown but execution is paused at: _run_module_as_main)
invalid argument: cannot get generic type information: typing.Optional[dict]: cannot get generic type information: dict[str, None]: invalid value type in dict: None is not a type

the object can dumps with orjson (orjson dumps to bytes ...)

out_bytes = orjson.dumps(msg)
out_txt = out_bytes.decode("utf-8")