def _next_raw_dimension(self):
        """_RawDimension for next *dimension_dict* in sequence or None for last.

        Returns None if this dimension is the last in sequence for this cube.
        """
        dimension_dicts = self._dimension_dicts
        this_idx = dimension_dicts.index(self._dimension_dict)
        if this_idx > len(dimension_dicts) - 2:
            return None
        return _RawDimension(dimension_dicts[this_idx + 1], self._dimension_dicts)