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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 default(self) -> Optional[ScalarValue]: """Default value of the receiver, if any."""

        if self.mandatory:
            return None
        if self._default is not None:
            return self._default
        return (None if self.type.default is None
                else ArrayValue([self.type.default]))