Can I discard a card to Unlicensed Armory with no friendly units in play?

Ruling: No, you cannot activate Unlicensed Armory with no friendly units in play. For all effects that target, you must have a legal target to activate the ability, even if the effect itself is not mandatory.

Nuances:

• The targeting requirement is not optional, even though the save effect itself is optional
• You also cannot activate Unlicensed Armory with no cards in hand, since "Discard 1" is a cost that must be paid to activate the ability