int sheetIndex = getWorkbook().getSheetIndex(this);
FormulaShifter shifter = FormulaShifter.createForRowShift(sheetIndex, startRow, endRow, n);
rowShifter.updateNamedRanges(shifter);
rowShifter.updateFormulas(shifter);
rowShifter.shiftMerged(startRow, endRow, n);
//rebuild the _rows map
TreeMap<Integer, XSSFRow> map = new TreeMap<Integer, XSSFRow>();
for(XSSFRow r : _rows.values()) {
map.put(r.getRowNum(), r);