My idea is that the default value is ```nil``` and a normal behavior - it is out from the application.

And if user don't want to change it then he not use ```:exit-on-close``` option. He just set ```:on-close``` or don't use anything from it. In this case ```(not (false? (:exit-on-close options)))``` return ```true```. Because ```(:exit-on-close options) == nil```.

Otherwise user set ```:exit-on-close``` in ```false``` and ```(not (false? (:exit-on-close options))) == false```