In any action or proceeding by or against any surviving partner or partners, or joint contractor or joint contractors, no adverse party or person adversely interested in the event thereof, shall, by virtue of Section 8-101 of this Act, be rendered a competent witness to testify to any admission or conversation by any deceased partner or joint contractor, unless some one or more of the surviving partners or joint contractors were also present at the time of such admission or conversation; and in every action or proceeding a party to the same who has contracted with an agent of the adverse party – the agent having since died – shall not be a competent witness as to any admission or conversation between himself or herself and such agent, unless such admission or conversation with the deceased agent was had or made in the presence of a surviving agent or agents of such adverse party, and then only except where the conditions are such that under the provisions of Sections 8-201 and 8-401 of this Act he or she would have been permitted to testify if the deceased person had been a principal and not an agent.