Going through customs they check ALL BAGGAGE AND ALL PASSPORTS ... not the partitive some baggage or some passports. Certainly not arbitrary. But 'les douanes vous permettent d'apporter des choses" .. not everything but the partitive article des things.
Actually, in a lot of countries the passport control is one branch of the state and customs another, entirely separate one. Probably best to check beforehand, if you're likely to be (unknowingly) carrying contraband.