docs: private static IndexedInts getRow(ColumnValueSelector s)
    {
      if (s instanceof DimensionSelector) {
        return ((DimensionSelector) s).getRow();
      } else if (s instanceof NilColumnValueSelector) {
        return ZeroIndexedInts.instance();
      } else {
        throw new ISE(
            "ColumnValueSelector[%s], only DimensionSelector or NilColumnValueSelector is supported",
            s.getClass()
        );
      }
    }