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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def update(cls, draft_share_invite_api_key_id, status=None, sub_status=None, expiration=None, custom_headers=None):
 """ Update a draft share invite. When sending status CANCELLED it is possible to cancel the draft share invite. :type user_id: int :type draft_share_invite_api_key_id: int :param status: The status of the draft share invite. Can be CANCELLED (the user cancels the draft share before it's used). :type status: str :param sub_status: The sub-status of the draft share invite. Can be NONE, ACCEPTED or REJECTED. :type sub_status: str :param expiration: The moment when this draft share invite expires. :type expiration: str :type custom_headers: dict[str, str]|None :rtype: BunqResponseDraftShareInviteApiKey """


        if custom_headers is None:
            custom_headers = {}

        api_client = client.ApiClient(cls._get_api_context())

        request_map = {
            cls.FIELD_STATUS: status,
            cls.FIELD_SUB_STATUS: sub_status,
            cls.FIELD_EXPIRATION: expiration
        }
        request_map_string = converter.class_to_json(request_map)
        request_map_string = cls._remove_field_for_request(request_map_string)

        request_bytes = request_map_string.encode()
        endpoint_url = cls._ENDPOINT_URL_UPDATE.format(cls._determine_user_id(),
                                                       draft_share_invite_api_key_id)
        response_raw = api_client.put(endpoint_url, request_bytes,
                                      custom_headers)

        return BunqResponseDraftShareInviteApiKey.cast_from_bunq_response(
            cls._from_json(response_raw, cls._OBJECT_TYPE_PUT)
        )