Shadow is filled even when the child widget is hollow

[aytunch]

First of all thank you for this nice package.

I have a svg widget which is like a circle outline (so empty in the inside)
When I use simple_shadow, the shadow is not an outline but it is filled in with grey color all the way.
this makes my circle child show the shadow through it's hole.
Is there a way to make the shadow the exact same shape as the widget without filling the insides?