(a) A waiver under this chapter shall be in writing and shall be signed by the surviving spouse.
(b) Subject to subdivision (c), a waiver under this chapter is enforceable only if it satisfies the requirements of subdivision (a) and is enforceable under either Section 143 or Section 144.
(c) Enforcement of the waiver against the surviving spouse is subject to the same defenses as enforcement of a contract, except that:
(1) Lack of consideration is not a defense to enforcement of the waiver.
(2) A minor intending to marry may make a waiver under this chapter as if married, but the waiver becomes effective only upon the marriage.