Can Unlicensed Armory be activated without a valid target, just to discard a card?

Ruling: No, Unlicensed Armory cannot be activated without a valid target unit. Cards that require targeting cannot be used without a legal target.

Nuances:

• "May" language alone (e.g., "you may kill a gear") is not sufficient to make targeting optional - the target is still required at activation, with the choice to execute the effect made only on resolution
• "Up to one" or "up to N" wording makes targeting optional, allowing activation without a target
• Salvage received errata to change from "may" to "up to one" specifically to allow optional targeting