CA Civ Code Section 8126

An oral or written statement purporting to waive, release, impair or otherwise adversely affect a lien or claim is void and unenforceable and does not create an estoppel or impairment of the lien or claim unless either of the following conditions is satisfied:

(a)

The statement is pursuant to a waiver and release under this article.

(b)

The claimant has actually received payment in full for the claim.