title: POI formula evaluator not working
body: <p>I use poi-ooxml 3.9 to generate invoice report from an excel template I store in db. I have formulas at the end of the sheet that will do sum and other tax calculations. </p>
  
  <blockquote>
  <pre><code>cell D30 =SUM(D22:D28) 
  cell D31 =D30*0.12 
  cell D32 =D31*0.02
  cell D33 =D31*0.01
  cell D35 =SUM(D30:D33)
  </code></pre>
  </blockquote>
  
  <p>Before I write the sheet to a new file I evaluate the formulas, but nothing works. The code below is used to evaluate the formulas. Do I need to evaluate the formulas whenever I write the values into the cells or only at the end of the operation?</p>
  
  <pre><code>String formulaCells[] = { "D30", "D31", "D32", "D33", "D35" };
  FormulaEvaluator formulaEvaluator = workBook.getCreationHelper()
          .createFormulaEvaluator();
  Sheet sheet = workBook.getSheetAt(0);
  for (String cellRef : formulaCells) {
  CellReference ref = new CellReference(cellRef);
  Row actualRow = sheet.getRow(ref.getRow());
  Cell cell = actualRow.getCell(ref.getCol());
  if (cell != null) {
  // here I evaluate the formula     
  formulaEvaluator.evaluateFormulaCell(cell);
  </code></pre>
  
  <p>anything I have missed? </p>
  
  <p>Note: Only after I open the generated sheet and press enter in every cells the formulas are evaluated!</p>