code: @Override
    public IndexedInts getRow()
    {
      final IndexedInts row = selector.getRow();
  
      if (row.size() == 1) {
        if (nullAdjustment == 0) {
          return row;
        } else {
          nullAdjustedRow.setValue(row.get(0) + nullAdjustment);
          return nullAdjustedRow;
        }
      } else {
        // Can't handle non-singly-valued rows in expressions.
        // Treat them as nulls until we think of something better to do.
        return ZeroIndexedInts.instance();
      }
    }
docs: Treats any non-single-valued row as a row containing a single null value, to ensure consistency with
  other expression selectors. See also {@link ExpressionSelectors#supplierFromDimensionSelector} for similar
  behavior.