What is the standard of review applicable to harmless error analysis?

We have noted "[t]here is some conflicting authority regarding the standard of review applicable to the harmless error analysis" in this context. Id. Indeed, in some cases we have "stated that a violation of a defendant's right to be present is not harmless if his 'absence created any reasonable possibility of prejudice,'" id. (quoting United States v. Fontanez 878 F.2d 33, 37 (2d Cir. 1989)), while in others "we have analyzed this type of case under a more deferential standard: whether the court can say with 'fair assurance . . . that the judgment was not substantially swayed by the error.'" Collins, 665 F.3d at 461 (quoting Krische v. Smith, 662 F.2d 177, 179 (2d Cir. 1981)). Nonetheless, we need not resolve this issue here because under either formulation there is no doubt that the error was harmless.