Hide Toon/Lighted Outline in the absence of light

I'm trying to show the outline of an object only when it is hit by a light source. The problem I'm currently facing is that, by using this built-in shader (Toon/Lighted Outline), only the main color responds to light, and the outline is allways visible even in complete darkness. (And I have removed the ambient lighing in preferences).

How can I also make the outline respond to light just like the main color does ?