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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, value):
 """Returns Series with missing values replaced with value. Parameters value : {int, float, bytes, bool} Scalar value to replace missing values with. Returns ------- Series With missing values replaced. """

        if not is_scalar(value):
            raise TypeError('Value to replace with is not a valid scalar')

        return Series(weld_replace(self.weld_expr,
                                   self.weld_type,
                                   default_missing_data_literal(self.weld_type),
                                   value),
                      self.index,
                      self.dtype,
                      self.name)