Abilities » Trade
Can I use Liepard's "Trade" Ability if there are no cards in my deck, just to discard a card?
No, you can't use Trade if there aren't any cards left in your deck. Discarding a card from your hand is a cost to use the Ability, and drawing cards is the effect.
Source: Brilliant Stars FAQ; TPCi Rules Team (2022-02-24)
Abilities » Trade
Can I use Zoroark GX's "Trade" Ability to discard a card from my hand if there are no cards left in my deck?
Yes you can. The first part of Trade is to discard a card from your hand, period. Then you do as much of the rest of the Ability as you are able to.
Source: TPCi Rules Team (2019-03-21)