title: Null-pointer exception in postProcessXLS method to export datable to spreadsheet
body: <p>Good day people. I am working on a java-ee project, specifically working on exporting a datable to spreadhseet(xls). I have a method called postProcessXLS. I use this method to auto adjust the column width of the generated spreadsheet and also to add cell styles and formatting. When i run the app, the method postProcessXLS throws a null pointer exception without referencing the line.</p>
  
  <p>bean</p>
  
  <pre><code> public void postProcessXLS(Object document) throws IOException,     BadElementException, DocumentException {
      try {
          HSSFWorkbook wb = (HSSFWorkbook)document;
          HSSFSheet sheet = wb.getSheetAt(0);
          HSSFRow header = sheet.getRow(0);
  
          HSSFCellStyle cellStyle = wb.createCellStyle();
          cellStyle.setFillForegroundColor(HSSFColor.GREEN.index);
          cellStyle.setFillPattern(HSSFCellStyle.SOLID_FOREGROUND);
  
          for (int i = 0; i &lt; header.getPhysicalNumberOfCells(); i++) {
              HSSFCell cell = header.getCell(i);
  
              cell.setCellStyle(cellStyle);
          }
  
          for (int colNum = 0; colNum &lt; header.getLastCellNum(); colNum++) {
              sheet.autoSizeColumn(colNum);
          }
      } catch (Exception ex) {
          LOG.error("Could not process spreadsheet" + ex);
      }
  }
  </code></pre>