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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 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)