When building a new world, I needed to be able to clear only one diamond from a players inventory when they died. When testing the command /clear @p[score_Deaths_min=1] diamond 1, it would say Could not clear the inventory of BZ_STEVE, no items to remove, even when I had a stack of diamonds in my inventory. I also tried this with just /clear @p diamond 1, for those of you who think it is because I hadn't died.