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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def fillna(self, series, addition=0):
 """ Fills with encoder specific default values. :param data: examined to determine defaults :param addition: uniquely identify this set of fillnas if necessary :return: filled data """

        if series.dtype == numpy.object:
            return series

        return series.fillna(self.missing_value + addition).astype(self.dtype)