A. After December 31, 1994, a person may enter into a contract to make a will or devise or not to revoke a will or devise or to die intestate only by:

1. 1. Provisions of a will that state the material provisions of the contract.
2. 2. An express reference in a will to a contract and extrinsic evidence proving the terms of the contract.
3. 3. A writing signed by the decedent evidencing the contract.