Get parameter value.

        If this cached value is None and this serialized value is not None,
        calculate the new value from the serialized one.

        :return: parameter value.
        :raises: TypeError if serialized value is not an instance of self ptype
            . ParserError if parsing step raised an error.

def value(self):
        """Get parameter value.

        If this cached value is None and this serialized value is not None,
        calculate the new value from the serialized one.

        :return: parameter value.
        :raises: TypeError if serialized value is not an instance of self ptype
            . ParserError if parsing step raised an error.
        """

        result = self._value

        if result is None and self._svalue is not None:

            try:
                result = self._value = self.resolve()

            except Exception as e:
                reraise(
                    Parameter.Error,
                    Parameter.Error('Call the method "resolve" first.')
                )

        return result