Well, I think you are mistaken, because Protection form Undead DOES exist. Only, it is not a spell you can learn, but a Protection Scroll (they have green icons) which you can buy and use in your Quick Item Slot.
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Melusine, High Queen of Fluffies, Archbabe of the Order of the Holy Flame and the Laughing Hyenas, &
Official Entertainer Elf of the BG2 Bar
Your voice is ambrosia