Fresh, good ilama seeds are definitely not empty or hollow--- they are full of stored carbohydrates, proteins, fats, vitamins, enzymes and minerals.
The embryo tends to not be well developed yet, and often is not yet visible to the naked eye. If you can see it, you will find it near the rough tip of the seed.
I suspect that, when the seed is developing in the young fruit, that mineral availabilities, such as of Calcium, Boron, and Zinc, determine whether or not the embryo will develop normally.