In a rei vindicatio action where the defendant's original right to occupy property was based on an employment contract, the plaintiff owner must prove the lawful termination of that employment contract, even if the plaintiff is not the employer, because the plaintiff entered into the lease arrangement on the basis of the employment relationship. Where there is a nexus between the lawfulness of occupation and the lawfulness of termination of employment, and a labour dispute concerning the termination is pending before a superior court, the rei vindicatio action should be postponed pending the determination of the labour dispute.