Include this card in your army only if all Deployment cards in your army are unique.

When one of your unique figures is defeated, you may draw 1 Command card, then place 1 Command card from your hand on the bottom of your deck .

So if I had 0 cards, I would draw one, but then be forced to immediately place it on the bottom of the deck?

No, I'd say if you have 0 cards, you wouldn't draw and therefore you wouldn't put one back.

The important word here is "THEN".

You only do the second part (in bold) if the first part is completed.

EDIT: This is for 0 cards in the deck not in your hand. I misunderstood your question.

Yes you must put one back if you draw one (and have no others in your hand).... but you don't have to draw one to begin with due to the word "may".

Do as much as you can. If you have 0 cards, you may draw 1, then put 1 to the bottom of the deck. If you draw 1, you will have one to place on the bottom. So you will probably not want to draw 1 in that case.

The key here is the effect is optional, so if you have 0, just don't use it.