(a) Real Party in Interest. Except for any action brought under General Laws, chapter 152, section 15, every action shall be prosecuted in the name of the real party in interest. A personal representative, guardian, conservator, bailee, trustee of an express trust, a party with whom or in whose name a contract has been made for the benefit of another, or a party authorized by statute may sue in his own name without joining with him the party for whose benefit the action is brought; and when a statute