Does the Attorney General have a duty to instruct a jury on the element of gang enhancement?

We need not consider whether defendant's claim of error is valid because, even if he was entitled to a jury finding on the age issue, the Attorney General has met his burden of showing that defendant did not suffer any prejudice from the trial court's failure to submit this issue to the jury. This type of error "is reversible . . . unless it can be shown 'beyond a reasonable doubt' that the error did not contribute to the jury's verdict." (People v. Sengpadychith (2001) 26 Cal.4th 316, 326 [failure to instruct jury on element of gang enhancement].)