def data(self):
        """
        NumPy array containing data if there is data for this object,
        otherwise None.
        """
        if self._data is None:
            # self._data is None if data segment is empty
            return np.empty((0, 1))
        if self._data_scaled is None:
            scale = scaling.get_scaling(self)
            if scale is None:
                self._data_scaled = self._data
            else:
                self._data_scaled = scale.scale(self._data)

        return self._data_scaled
NumPy array containing data if there is data for this object,
        otherwise None.