I don't know if I have something in there that was typed wrong, or if I am using the wrong tag to identify the entity stored inside the block. So far none of them have worked for me. May be they removed the ability to do that? I have no idea, but if anyone knows how to get this to work that would be great.
EDIT: I am trying to get a blank spawner, which is why I left the area where you would specify the entity blank.