So because you can't see his spirit in the helmet, the spirit IS the helmet?
Do you have any idea how stupid you sound?
Goron already explained his spirit is contained within the armor itself. Up until Arthas came along, Ner'zhul was just a trapped spirit without a body. Once he showed up to put on the armor, their two entities combined to take on the physical embodiment of the Lich King.
He's agreeing with you, I don't know why you're being such an idiot.