Can a judge overturn a finding that a district attorney improperly prosecuted a defendant on grounds of bias?

We recently confronted an analogous issue in People v. Hedgecock (1988) 201 Cal.App.3d 174. There, the trial court erroneously denied the defendant an evidentiary hearing on whether the district attorney should be disqualified on grounds of bias. We nonetheless affirmed defendant's conviction because he failed to point to any facts indicating he had been prejudiced by the district attorney's prosecution of the case. "Courts will not undo a fair trial because of an erroneous pretrial legal ruling which had no effect on the outcome. [p] ... It is too late for [the defendant] to be relieved of the 'reasonable possibility' the district attorney's office might not act impartially in its conduct of the trial and related proceedings. Simply put, we cannot reverse where the 'reasonable possibility' never came to fruition." (Id. at p. 259.)