Feathering an Image Mask?

Hi, I have a very simple goal, but it's oddly difficult in FCPX. I have this image mask, and I want to apply feathering to it, but there's no slider/option for it in the image mask effect that comes with FCPX. Any free alternative plugins, or better yet, a native way to do it within FCPX?

Thanks in advance!

Hey Triple.

In my version of FCP, 10.4.3, I have a feather selection. This is with the Draw Mask applied:

Yes but I'm talking about the image mask. Unless there's a way to copy paste that into the draw mask...

The picture posted there IS the stock "Draw Mask" that comes with FCPX 10.4.
But you want to use the Shape Mask, and I understand, I use it often myself. It does not have a featuring option, which is a shame.

My work around is to apply a gaussian blur to a copy of my source image, using Pixelmator (or Photoshop or whatever). Then use that as the source of my shape mask.