code: def cbday_roll(self):
          
          cbday = CustomBusinessDay(n=self.n, normalize=False, **self.kwds)
  
          if self._prefix.endswith('S'):
              # MonthBegin
              roll_func = cbday.rollforward
          else:
              # MonthEnd
              roll_func = cbday.rollback
          return roll_func
docs: Define default roll function to be called in apply method.