New to Java

Hi ,
Iam using poi to read excel sheet. Iam reading line by line of excel sheet using HssfUserModel.
Here is my code

int numberOfRows = sheet.getLastRowNum();
for (int i = 1; i <= numberOfRows; i++)
 {

  HSSFRow row = sheet.getRow(i);
//  check whether row is null or not
  if (row != null)
   {
    int numberOfCells = row.getLastCellNum();
				
     for(int j=0;j <= numberOfCells;j++)
     {
         HSSFCell cell = row.getCell((short)j);
         short cellNumber = cell.getCellNum();
	 //check whether cell is null or not
          if(cell!=null)
          {
            if(cellNumber ==  myTradeConstants.scripCode_column_Number)
              {
               cell =row.getCell(myTradeConstants.scripCode_column_Number);
               scripCode =cell.getStringCellValue();
               System.out.println("scripCode:"+scripCode);
             }
	 }
        else
         {
              System.out.println("nocellValue");
              break;
         }
      } 
  }
else 
{
   System.out.println("rowBreak");
   break;
}

My Excel sheet is also having so many number of rows. But it is displaying only first row of the excel sheet. n displaying "nullpointerException".
why iam getting nullPointer Exception.

I want to check whether a cell is having data or not.
can anybody guide me in right dircection.

regards,
ramu.