Does a reference to a defendant's failure to testify constitute a harmless error?

Notwithstanding the foregoing, even if we were to presume error, it was not prejudicial. "[Griffin] error requires reversal unless we can conclude it was harmless beyond a reasonable doubt. [Citations.]... [W]e ask whether, absent the prosecutor's reference to [the defendant's failure to testify, is it clear beyond a reasonable doubt that the jury would have returned a verdict of guilty? [Citation.]" (People v. Hardy (1992) 2 Cal.4th 86, 154.) [I]ndirect, brief and mild references to a defendant's failure to testify, without any suggestion that an inference of guilt be drawn therefrom, are uniformly held to constitute harmless error." ' [Citations.]" (People v. Boyette (2002) 29 Cal.4th 381, 455-456, fn. omitted.)