In a new Eberron game, my DM suggested that I consider taking the Aberrant Dragonmark feat. It suits me well, as I initially wanted to take Magic Initiate.
However, one word in the description is bugging me. It says that when I cast the 1st-level spell, I "can" expend a Hit Die (emphasis mine):
When you cast the 1st-level spell through your mark, you can expend one of your Hit Dice and roll it.
Must I expend one Hit Die if I'm able to?
What happens if I don't want to?
What happens if I don't have any Hit Die left?
Usually the wording says "you may" and provides further wording if I do or if I don't (or both), but here there's no such stances. So I'm at a loss on how to properly understand the requirement of casting a 1st-level spell with the Aberrant Dragonmark feat.