When a partnership, the business of which is transacted by one or more of the partners exclusively, or by an agent or agents, is named as garnishee, service may be made upon such partnership by leaving a true and attested copy of the process with, or at the usual place of abode of, the members of such partnership, or such acting partner or partners, agent or agents; and the plaintiff, at any time before final judgment in such suit, may amend such process, without costs, by inserting the names of the persons composing such partnership.