Where a person negotiates or transfers a document of title for value otherwise than as a mere intermediary under Code Section 11-7-508, then unless otherwise agreed he warrants to his immediate purchaser only in addition to any warranty made in selling the goods:

(a) That the document is genuine; and

(b) That he has no knowledge of any fact which would impair its validity or worth; and

(c) That his negotiation or transfer is rightful and fully effective with respect to the title to the document and the goods it represents.