def add_handler(self, handler, args=None, kwargs=None):
        """
        Registers a new handler.

        :param handler: handler to register.
        :type handler: :class:`fatbotslim.handlers.BaseHandler`
        :param args: positional arguments to pass to the handler's constructor.
        :type args: list
        :param kwargs: keyword arguments to pass to the handler's constructor.
        :type kwargs: dict
        """
        args = [] if args is None else args
        kwargs = {} if kwargs is None else kwargs
        handler_instance = handler(self, *args, **kwargs)
        if isinstance(handler_instance, RightsHandler):
            self.rights = handler_instance
        if handler_instance not in self.handlers:
            self.handlers.append(handler_instance)
Registers a new handler.

        :param handler: handler to register.
        :type handler: :class:`fatbotslim.handlers.BaseHandler`
        :param args: positional arguments to pass to the handler's constructor.
        :type args: list
        :param kwargs: keyword arguments to pass to the handler's constructor.
        :type kwargs: dict