Action to annul an arbitral award. Abstention from voting by one of the co-arbitrators on the merits of the dispute. Prevalence of the presiding arbitrator's vote. Impossibility of abstention by the co-arbitrator. Violation of Article 5, XXXV, of the Federal Constitution. Prohibition, by analogy, of the "non liquet". Nullity of the arbitral award and submission of the dispute to a new arbitral proceeding, ordering the co-arbitrator not to abstain, under penalty of replacement: