def get_task_fs(self, courseid, taskid):
        """
        :param courseid: the course id of the course
        :param taskid: the task id of the task
        :raise InvalidNameException
        :return: A FileSystemProvider to the folder containing the task files
        """
        if not id_checker(courseid):
            raise InvalidNameException("Course with invalid name: " + courseid)
        if not id_checker(taskid):
            raise InvalidNameException("Task with invalid name: " + taskid)
        return self._filesystem.from_subfolder(courseid).from_subfolder(taskid)
:param courseid: the course id of the course
        :param taskid: the task id of the task
        :raise InvalidNameException
        :return: A FileSystemProvider to the folder containing the task files