The basis of legal positivism is that a law’s merit does not influence its existence. In other words, the law’s injustice or immorality does not negate its existence. The law is what it has been posited to be in authoritative sources (e.g. legislation or judicial decisions). Although legal positivism does not necessarily favour parliamentary statutes as opposed to judge-made law, the principle of legality was historically developed in connection with the codification movement after the French Revolution (…). The codification process – led by Portalis – aimed specifically at limiting judicial powers, in addition to the violence and anarchy of the French Revolution itself.
(The principle of legality in European criminal law, Intersentia, la p. 66)