What do you think of the "incest baby" theory?

The theory that the Night's King is invading human space because he didn't get the incest baby he was promised, because Gilly took him to be with Sam, instead of sacrificing him to the White Walkers? And that means the ancient treaty between the humans and the Night's King was broken?

Personally, if all the NK wants is an incest baby, I think they should hand over Cersei's.