def model(self, value):
        """The model property.
        
        Args:
            value (string). the property value.
        """
        if value == self._defaults['ai.device.model'] and 'ai.device.model' in self._values:
            del self._values['ai.device.model']
        else:
            self._values['ai.device.model'] = value
The model property.
        
        Args:
            value (string). the property value.