This is from the 2016 Devas v. India Award (some footnotes omitted):
219. Indeed, it is well established by judgments of the International Court of Justice (the “ICJ”) and investment arbitration awards that, unless a treaty contains specific wording granting full discretion to the State to determine what it considers necessary for the protection of its security interests,286 national security clauses are not self-judging.
286 Self-judging “essential security interests” provisions are far from being unknown in international law. See, for instance, Article XXI of the General Agreement on Tariffs and Trade 1947 (“GATT”): “Nothing in this Agreement shall be construed: (a) to require any contracting party to furnish any information the disclosure of which it considers contrary to its essential security interests; or (b) to prevent any contracting party from taking any action which it considers necessary for the protection of its essential security interests…” ...
There's not much relevance here for a WTO panel or the Appellate Body considering the issue as part of a WTO complaint, but I thought it was worth noting.