Default desktop wallpapers have disappeared

My desktop wallpaper just disappeared on its own, at first I thought maybe it needed an update and there was a new update for my mac (I am using a Macbook pro retina 13 inch - 2014) but even after installing the update, my wallpaper won't go back. It is a solid colour now and I can't even view the default apple wallpapers. Suggestions are welcome. Thank you.