Can a jury impose a sentence of life imprisonment without parole even if it finds no mitigating evidence?

2. Absence of Mitigation. Defendant contends the trial court erred in failing to instruct sua sponte that the jury could impose a sentence of life imprisonment without parole even if it found no circumstances in mitigation. (See People v. Duncan, supra, 53 Cal.3d 955, 979, 281 Cal.Rptr. 273, 810 P.2d 131 ["The jury may decide, even in the absence of mitigating evidence, that the aggravating evidence is not comparatively substantial enough to warrant death."].) Defendant insists that the lack of such an instruction violated his right to due process and to a reliable penalty determination under the federal Constitution, and denied him equal protection of the law under the federal and state Constitutions. We reject the claim.