for (int i = 0; i < this.datasetInfo.size(); i++) {
            SeriesDataset child = getDatasetInfo(i).data;
            if (child instanceof CombinationDataset) {
                SeriesDataset childParent 
                    = ((CombinationDataset) child).getParent();
                if (parent == null) {
                    parent = childParent;
                }
                else if (parent != childParent) {
                    return null;
                }
            }
            else {
                return null;