Is a defendant's sentence challenge based on Penal Code section 654 a challenge that affects the validity of his no contest pleas?

The crucial question here, disputed by the parties, is whether defendant's sentence challenge based on Penal Code section 654's prohibition against multiple punishment is a challenge that affects the validity of his no contest pleas. "[A] challenge to a negotiated sentence imposed as part of a plea bargain is properly viewed as a challenge to the validity of the plea itself" and thus requires a certificate of probable cause. (People v. Panizzon (1996) 13 Cal.4th 68, 79, 51 Cal.Rptr.2d 851, 913 P.2d 1061.)