There's a presumption either way. You can make the presumption JS did for [] (and there's probably no turning back), you can even argue explicit is better than implicit (vs the value of context-sensitive concision).

But it's also not consistent with the ways that other empty but typed cups are treated ("" for the empty string, 0 for empty count / quantity, both of which are false-y). Different presumptions for different types of cups carries its own implicit hazards from context sensitivity.