Your proposal would break all of logic and mathematics. "All marbles in the bag are black" is equivalent to "For all x, if x is a marble and x is in the bag, t

Your proposal would break all of logic and mathematics. "All marbles in the bag are black" is equivalent to "For all x, if x is a marble and x is in the bag, then x is black". Since the antecedent is false if the bag is empty, the statement is true by material implication.