Blake Shelton might have a little competition on one of his biggest hits with Gwen Stefani!During Tuesday's season 19 finale of Gwen was joined on stage by her finalist, 15-year-old Carter Rubin, and the pair performed «You Make It Feel Like Christmas» off of her 2017 holiday album of the same name.«How big are the shoes, 'cause I've heard he's really tall?» Carter joked of filling Blake's shoes on the duet«I am excited to sing with Carter, because he's so unbelievably talented and he's gonna