First question: Can you "would gain" something if that supply pile is empty? For instance, if another player plays Witch and the Curse pile is empty, can I reveal Trader and gain a Silver instead of the nothing I would have gained if I don't?
If the answer is "No", then I think that's odd, but ok. If the answer is "Yes", then the FAQ for Embargo is incorrect (I'm reading for the Wiki, so maybe is not an official FAQ, but all this time I was assuming they all are):
If there are no Curses left, Embargo tokens do nothing.
because I should be able to gain extra Silvers from Trader if I buy something from an Embargo'ed pile.
While we are on the embargo edge case topic, can I (attempt to) buy something from an empty embargoed pile and gain a Curse from Embargo? (for instance, there is a pile embargoed twice and two Curses left and I have only one buy and more than 2 VP lead, so I want to end the game)