Does a failure to give diminished capacity-involuntary manslaughter instruction in a second degree murder case constitute a prejudicial error?

In People v. Roberts (1975) 51 Cal.App.3d 125, 133, 123 Cal.Rptr. 893, and People v. Matta (1976) 57 Cal.App.3d 472, 482-484, 129 Cal.Rptr. 205, the courts determined that the failure of the respective trial courts to give the diminished capacity-involuntary manslaughter instruction while error, was not prejudicial error because the jury in convicting the defendants of second degree murder, impliedly found malice aforethought, which impliedly determined the factual question presented by the missing instruction adversely to defendant under properly given instructions.