Where a person negotiates or delivers a document for value otherwise than as a mere intermediary under § 8.7-508, then, unless otherwise agreed, he warrants to his immediate purchaser, in addition to any warranty made in selling or leasing the goods, that:
(a) the document is genuine; and
(b) he has no knowledge of any fact that would impair the document's validity or worth; and
(c) his negotiation or delivery is rightful and fully effective with respect to the title to the document and the goods it represents.