title: I need to iterate to the end of a column in Java on an Excel Sheet with Apache POI
body: <p>I am iterating down a column of values until it hits a blank. I need to gather the entire column and store it, and no other values. I've attempted to check for blank, null, 0, "", and CELL_TYPE_BLANK (int = 3), and I cannot get it to avoid a null pointer exception. Code snippet and error are below. What can I do? This is not the entire method or program, just the relevant piece.<P></p>
  
  <pre><code>String s = list[i];
  //find the directory from the list array to locate the file
  InputStream input = new FileInputStream(s);
  //create a new workbook object to hold the excel file
  Workbook wb = new XSSFWorkbook(input);
  //create an arbitrary starting location
  int column = 2; //absolutely the correct number
  int rownum = 10;
  //get the value from the first sheet
  org.apache.poi.ss.usermodel.Sheet insheet = wb.getSheetAt(0);       
  //of the second columm
  Row row = insheet.getRow(rownum);
  //in the 11th row (arbitrary number used to reduce iterations and skip whitespace)
  Cell cell = row.getCell(column); 
  System.out.println("Skimming sheet: " + insheet.getSheetName());
  //iterate until the very end of the column is found
  System.out.println("Cell value B" + (rownum-1) +  ": " + cell);
  
  //3 denotes CELL_TYPE_BLANK
  while (cell.getCellType() != 3 ) {
      //go to the next location
      //update to the next cell
      System.out.println("Cell value B" + rownum +  ": " + cell);
      row = insheet.getRow(rownum);
      if(row.getCell(column).getCellType() != 3){
          cell = row.getCell(column); //error occurs here, line 241
      }
      rownum++;
  }
  
  
  Exception in thread "main" java.lang.NullPointerException
      at FileTest.skim(FileTest.java:241)
      at FileTest.main(FileTest.java:121)
  </code></pre>