I've had the same issue.
When using a card like Humiliate with the "Expend from Que" effect, if there is no available card to expend, you have no way to progress.
This can be performed by:
1. Using the card "Pump Up" Build Ability to add Expend to a card.
2. Play both cards with the expend ability in the same round with one being the last card you play
3. Expend the opponents last card
There will then be no card to target and no option to skip.
Also: How can you have a card with an effective cost of 15LP, and when its played it does nothing but show a popup saying "doesn't work on boss?!?!?!"