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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_command(self, command, args=None):
 """ Updates the callback command which is called when the ButtonGroup changes. Setting to `None` stops the callback. :param callback command: The callback function to call. :param callback args: A list of arguments to pass to the widgets `command`, defaults to `None`. """

        if command is None:
            self._command = lambda: None
        else:
            if args is None:
                self._command = command
            else:
                self._command = utils.with_args(command, *args)