return a nil error for a before adviced function

[mathews]

beyond is really good.
But when I use a before advice, and set the returning Args, I just failed to reurn a nil error. I tried to not set the returning error, or set the nil return Args with SetWithType, either way will cause go panic. I MUST set a not-nil error, evenif the function returns successfully.
Is there a way to return a nil Arg for a before advice?
much thanks.