Normally it's unlikely, if not impossible, for this to happen, however I have come across a combo that may cause an issue. If a character has resistance to Necrotic damage and is cursed with vulnerability, the damage is usually halved, then doubled, effectively rounding odd amounts of damage down by 1 (both a 6 and a 7 would deal 6 necrotic damage for example.) If a creature has Immunity though, such as a ghost, you expect the damage to be reduced to 0 before being doubled, and double 0 is still 0.
The other option I can think of though, due to the existence of the Dragon Masks that basically upgrade resistance to the appropriate element to immunity. Could you treat the above mentioned curse that way?
I should mention that the curse is from a magic item found in an Adventurers League approved book, thus this may actually become an issue, even in AL games.
