Al was named the beneficiary in his mother’s life insurance policy. His mother died during the contestable period. The insurer denied payment, citing a material misrepresentation on the application. Al believes the insurer should pay the claim because the misrepresentation occurred on the application, and the application is not part of the formal agreement between the insurer and the policyholder. Which provision protects the insurer by making the application part of the formal agreement between the parties to the contract?