method frame_by_id may return None, which is not checked against self

[daemonPainter]

I submit for consideration the following:

    def frame_by_id(self, arbitration_id):  # type: (ArbitrationId) -> typing.Union[Frame, None]
        """Get Frame by its arbitration id.

        :param ArbitrationId arbitration_id: Frame id as canmatrix.ArbitrationId
        :rtype: Frame or None
        """
        hash_name = f"{arbitration_id.id}_{arbitration_id.extended}"
        
        frame = self._frames_dict_id_extend.get(hash_name, None)
        if frame is not None:
            return frame
        for frame in self.frames:
            if frame.arbitration_id == arbitration_id:
                # found ID while ignoring extended or standard
                self._frames_dict_id_extend[hash_name] = frame
                return frame
        return None

which is called later on as

    def encode(self,
               frame_id: ArbitrationId,
               data: typing.Mapping[str, typing.Any]
               ) -> bytes:
        """Return a byte string containing the values from data packed
        according to the frame format.

        :param frame_id: frame id
        :param data: data dictionary
        :return: A byte string of the packed values.
        """
        return self.frame_by_id(frame_id).encode(data)

It may happen that None is returned, therefore resulting in

AttributeError: 'NoneType' object has no attribute 'encode'

which is a situation that should (?) be safeguarded?