(a) Notwithstanding any other provision of this part, if a creditor makes a written demand for payment within the time specified in Section 19100, the trustee may waive formal defects and elect to treat the demand as a claim that is filed and established under this part by paying the amount demanded.
(b) Nothing in this section limits application of the doctrines of waiver, estoppel, laches, or detrimental reliance or any other equitable principle.