Can't Find Error: NullPointerException

Question

I'm getting a NullPointerException and looked up the error and read about it, but still can't seem to fix the problem. My main method takes a list of File types and Strings and passes it to the Parse method to convert Excel Files to txt Files. I'm fairly new to java, any help would be appreciated. Thanks!

Exception in thread "main" java.lang.NullPointerException
    at transform.Parse.Transform(Parse.java:54)
    at transform.Input.main(Input.java:62)

And here is my code. I put two comments where the exceptions are shown:

package transform;

public class Input {

    private static final Object Face_value = null;

    public static void main( String args[] ) throws Exception {

        String str = " "; 
        Scanner sc = new Scanner(System.in);
        ArrayList<String> ExcelList = new ArrayList<String>();    
        System.out.println("Print .xlsx file names");
            while (sc.hasNextLine() && !(str = sc.nextLine()).equals("")) {
                ExcelList.add(str);
            } 

          for(int i=0; i<ExcelList.size(); i++) {
              System.out.println(ExcelList.get(i));
          }

        String str1 = " ";
        Scanner sc1 = new Scanner(System.in);
        ArrayList<String> txtList = new ArrayList<String>();
        System.out.println("Print desired .txt file names");  
        while(sc1.hasNextLine() && !(str1 = sc1.nextLine()).equals("")) {
            txtList.add(str1);
        }

        if(txtList.size() != ExcelList.size()) {
            System.out.println("The number of Excel files listed does not match the number of .txt files listed");
        }

        for(int i=0; i < txtList.size(); i++) {
            System.out.println(txtList.get(i));
        }

        //convert ArrayList of type String to type File
        for(int i=0; i < ExcelList.size(); i++) {
            File file = new File(ExcelList.get(i));
            Parse.Transform(file, txtList.get(i));
        }  
         ///////////////////////////////////////////////////////////////////   
         //ERROR ON THE LINE ABOVE(line 62) -- Parse.Transform(file, txtList.get(i));
         ///////////////////////////////////////////////////////////////////
         /////////////////////////////////////////////////////////////////// 
        System.out.println("\nDone");

}
 }




 package transform;

public class Parse{

public static void Transform (File ExcelFile, String TxtFile) {
Writer writer = null;

try {

        //read excel file and get the first sheet
        FileInputStream fis = new FileInputStream(ExcelFile);
        XSSFWorkbook wb = new XSSFWorkbook(fis);
        XSSFSheet sheet = wb.getSheetAt(0);

        // set the name of the .txt file
        File file = new File(TxtFile);        
        writer = new BufferedWriter(new FileWriter(file));
        Iterator rows = sheet.rowIterator();
        writer.write("@SecurityDeal\r\n");

      while( rows.hasNext() ) {
         XSSFRow row = (XSSFRow) rows.next();

         if(row.getRowNum() == 0){
           continue;
         }

          Iterator cells = row.cellIterator();

          XSSFCell Face_Value = row.getCell(10); 
          XSSFCell Rate = row.getCell(8);
          XSSFCell DealDate = row.getCell(6);
          XSSFCell MaturityDate = row.getCell(7);
          XSSFCell CReference = row.getCell(5);
          XSSFCell Comments = row.getCell(4);

          XSSFCell Counterparty = row.getCell(3);
         //////////////////////ERROR ON BELOW LINE(Line 54) ///////////////////////
         ////////////////////////////////////////////////////////////////
         ////////////////////////////////////////////////////////////////
         String Cp = Counterparty.toString(); 

          //convert date to correct format
          Date s1 = MaturityDate.getDateCellValue();
          SimpleDateFormat sdf = new SimpleDateFormat("M/dd/yyyy");
          String MD = sdf.format(s1);

          Date d1 = DealDate.getDateCellValue();
          SimpleDateFormat sdf1 = new SimpleDateFormat("M/dd/yyyy");
          String dd = sdf1.format(d1);


          //convert cells to String
          String Comments_String = Comments.toString();
          String Face_Value_String = Face_Value.toString();

          //convert strings to double
          double Number_Comments = Double.parseDouble(Comments_String);
          double Number_Face_Value = Double.parseDouble(Face_Value_String);

          //get rid of exponential format
          String Comments1 = String.format("%.0f", Number_Comments);
          String Face_Value1 = String.format("%.0f", Number_Face_Value);

          //Mapping for counterparty
          if(Cp.equals("CITI")){
             Cp = "US-Citibank, US";
          }
          else if(Cp.equals("BAML")){
             Cp = "US-Bank Of America Merrill Lynch";
          } 
          else if (Cp.equals("MIZUHO")) {
             Cp = "US-Mizuho Ltd";
          }
          else if(Cp.equals("WELLS")) {
             Cp = "US-Wells Fargo";                  
          }


          writer.write("$NEW\r\n" + "Instrument=US-Commercial Paper\r\n" + "BorrowInvest=BORROWING\r\n"
          + "Counterparty=" + Cp + "\r\n" + "Entity=US-GMF\r\n" + "Currency=USD\r\n" + "FaceValue=" + Face_Value1 + "\r\n"
          + "BaseRate=" + Rate + "\r\n" + "DealDate=" + dd + "\r\n" + "MaturityDate=" + MD + "\r\n" + "Dealer=GM_Financi\r\n" + 
          "CounterpartyReference=" + CReference + "\r\n" + "Comments=" + Comments1 + "\r\n$INSERT\r\n");  

          System.out.println("\r\n");
      }
      System.out.println("Successfully Created File");  
} catch ( IOException ex ) {
    ex.printStackTrace();
    System.out.println("Check formatting of file names. Make sure they end in .txt or .xlsx");
    } finally {
        try 
            {if (writer != null) {writer.close();}} 
                catch (IOException e) {e.printStackTrace();}
   }
  }
 }