Contract to make a will, not to revoke a will or to die intestate

(1) A contract to make a will or devise, or not to revoke a will or devise or to die intestate, if executed after June 16, 1972, can be established only by: (a) Provisions of a will stating material provisions of the contract; (b) An express reference in a will to a contract and extrinsic evidence proving the terms of the contract; or (c) A writing signed by the decedent evidencing the contract. (2) The execution of a joint will or mutual wills gives rise to no presumption of a contract not to revoke the will or wills.