Cal. Gov. Code § 50307

It is against public policy to permit a person to waive the benefit of any provision of this article. A person shall not waive a right of action accruing to him pursuant to this article or any right he has as to the place of commencement or trial of the action. A person may waive a right accruing under Section 50305 with respect to unimproved real property or with respect to any parcel of real property if the parcel is sold or leased by the local agency to the State or to a county, city, district, or political subdivision.