title: Unable to insert data using POI for null values in excel sheet
body: <p>I'm trying to find a blank value in excel (xlsx) sheet and replace with some string like "ENTER VALUE" using my program with Apache POI library as below</p>
  
  <p>I'm able to read and identify blank/null values in excel sheet but couldnt insert any value into those cells</p>
  
  <pre><code>public static void main(String args[]) throws IOException, InvalidFormatException
      {
  
  
  
                  FileInputStream inputFile = new FileInputStream("//Users//suk//Documents/tes//testexcel.xlsx");
  
          //now initializing the Workbook with this inputFie
  
  
          // Create workbook using WorkbookFactory util method
  
           Workbook wb = WorkbookFactory.create(inputFile);
  
           // creating helper for writing cells
  
           CreationHelper createHelper = wb.getCreationHelper();
  
          // setting the workbook to handle null
  
           wb.setMissingCellPolicy(Row.CREATE_NULL_AS_BLANK);
  
  
          Sheet sheet = wb.getSheetAt(0);
  
  
          for (Row row : sheet) {
              int lastCellNo =row.getLastCellNum();
              int firstCellNo=row.getFirstCellNum();
  
              int rowNo =row.getRowNum();
              System.out.println(" row number = "+rowNo);
              System.out.println(" last cell no = "+lastCellNo);
  
  
              for(int i=firstCellNo;i&lt;lastCellNo;i++){
                  System.out.println("************");
  
                  Cell cell = row.getCell(i);
                  int colIndex =cell.getColumnIndex();
                  if(cell==null)
                  {
                      System.out.println(" The Cell:"+colIndex+" for row "+row.getRowNum()+" is NULL");
                  }
  
  
  
  
                System.out.println(" column  index  = "+colIndex);
  
  
               int cellType = cell.getCellType();
               System.out.println(" cell type ="+cellType);
  
               // writing a switch case statement
  
               switch(cellType)
               {
  
               case 0:
               {
                  double numValue = cell.getNumericCellValue();
                  //System.out.println(numValue);
                   break;
               }
               case 1:
               {
                   String cellString = cell.getStringCellValue();
                   System.out.println("----String value = "+cellString+"---String length ="+cellString.length());
  
                   // here checking null consition
  
              /*   if(cellString == null || cellString.equalsIgnoreCase("") || cellString.length()&lt;=0 || cellString.equalsIgnoreCase(" "))
                   {
                       // here creating the cell value after last cell
  
  
                   } */
                   break;
               }
               case 4:
               {
                    boolean bolValue =cell.getBooleanCellValue();
                    //System.out.println(bolValue);
                    break;
               }
  
               // for case of blank cell
  
               case 3:
               {
  
                   //int lastCellPlus =lastCellNo+1;
                   //System.out.println("last+1 column ="+lastCellPlus);
                   //row.createCell(lastCellPlus).setCellValue(" NULL VALUE..PLEASE ENTER VALUE ");
  
                   System.out.println(" cell details = "+cell.getColumnIndex()+" row details ="+row.getRowNum());
                   cell.setCellValue(createHelper.createRichTextString("ENTER VALUE"));
                   System.out.println(" Sucessfully written error");
  
                    break;
               }
  
  
               default: 
                   System.out.println(" unknown format");
                   break;
  
               }// switch
  
            } // row and cell iterator
  
  
            }
          }
  </code></pre>
  
  <p>}</p>
  
  <p>Below is the bit of code by which im identifying its Blank/Null value and trying to insert String but its not writing to that cell</p>
  
  <pre><code>case 3:
               {
  
                   //int lastCellPlus =lastCellNo+1;
                   //System.out.println("last+1 column ="+lastCellPlus);
                   //row.createCell(lastCellPlus).setCellValue(" NULL VALUE..PLEASE ENTER VALUE ");
  
                   System.out.println(" cell details = "+cell.getColumnIndex()+" row details ="+row.getRowNum());
                   cell.setCellValue(createHelper.createRichTextString("ENTER VALUE"));
                   System.out.println(" Sucessfully written error");
  
                    break;
               }
  </code></pre>