Fix: handle null lore properly

[Tiakin]

If an item is created without modifying its lore, its lore is automatically set to null rather than retaining that of the base item.

I made this change because, in the Walshy/mc-1.21 branch of Slimefun, when using the Altar, the lore gets removed since the empty lore overrides the base item's lore. I believe it's more appropriate to apply the fix here rather than in Slimefun, but I've prepared the other fix just in case.