Declaratory action for nullity of an arbitration award concerning a real property purchase and sale agreement. Allegation of impediment of the arbitrator who carried out the same activity as the appellee. Preclusion of raising the impediment objection in the arbitration proceedings, as it was only alleged upon the rendering of the award. Nullity of the arbitration award for denial of due process, given that the party was prevented from conducting an accounting expert examination that would prove the substantial performance of the obligation: