(a) The following persons may sue without joining as parties the persons for whose benefit the action is prosecuted:
(1) A personal representative, as defined in subdivision (a) of Section 58 of the Probate Code.
(2) A trustee of an express trust.
(3) Except for a person upon whom a power of sale has been conferred pursuant to a deed of trust or mortgage, a person with whom, or in whose name, a contract is made for the benefit of another.
(4) Any other person expressly authorized by statute.
(b) Notwithstanding subdivision (a), a trustee upon whom a power of sale has been conferred pursuant to a deed of trust or mortgage may sue to exercise the trustee’s powers and duties pursuant to Chapter 2 (commencing with Section 2920) of Title 14 of Part 4 of Division 3 of the Civil Code.