What does it mean when you dream about a person who's face you cannot see but you are so happy to see the person?

Good question. I think it depends on the context of the dream. There's not a lot to go on here. If you were in a perilous situation, it would be good to see anybody that could help. If things were calm or neutral, it could mean the faceless person was the embodiment of a person's greatest attributes, or at least the ones you find most appealing.