Slider only posts having featured image

Hello Ron. Congratulations for your job!!
First, sorry for my English, i’m Spanish person.
I’m building a little project in WordPress with your Frontier Theme. It’s posible setting the slider to show only post having featured image? Are there any code to this?
I don’t like that the slider show a white frame in post without featured imagen, and your idea for a default image is good, but I prefer don’t show this post.
Thanks.