I created an Armor Stand and I can't place any armor on it. I have diamond armor. I didn't try any other armor types. I tried each of the 4 pieces of armor by placing them in my hotbar, switching to them, and right clicking on the stand. Nothing happens. 

While doing this, I accidentally tried this with a torch in my hand, and it put the torch in the hand on the Armor Stand. So I'm not sure why it won't work with my actual armor.