Action to annul an arbitral award filed by the guarantors of the lease agreement. Nullity of the award declared because "the arbitration clause constitutes a form of preliminary contract, as a promise to enter into the definitive contract, i.e., the agreement to arbitrate." The failure to execute an agreement to arbitrate, notwithstanding the party having been notified, renders the proceedings and the arbitral award null and void. A defect that also taints due process of law: