I see this one pop up in the forum a lot and it's a pretty simple fix. All that's needed to it add some css to the bottom of your stylesheet - cut and paste style. Here it is:

It's a surprise that the app itself doesn't have a setting to handle this as you'd expect it to be a common request. No one wants to litter their entire site with zero based review stars. It's just not a good look. Could the appearance of nothing but empty or zero based reviews hurt those conversions - maybe. You'll need to test the conversion results yourself but at least the css is simple to add / remove as needed.

Any issues drop me a line in the comments below.