how to clear this programming error in getCellData in keyword driven framework for selenium webdriver?

Question

I'm using this program in Keyword driven framework for selenium web driver tool. But due to this program i'm getting null pointer exception every time i tried to debug the code but cant find any solution. please suggest me the solution for that error.

package utility;
import java.io.File;
import java.io.FileInputStream;
import java.util.ArrayList;
import java.util.List;



import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFRow;
import org.apache.poi.hssf.usermodel.HSSFSheet;
import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.hssf.usermodel.HSSFCell;
import org.apache.poi.hssf.usermodel.HSSFRow;

public class ExcelUtils {

  private static HSSFSheet ExcelWSheet;
  private static HSSFWorkbook ExcelWBook;
  private static HSSFCell Cell;

 //This method is to set the File path and to open the Excel file
 //Pass Excel Path and SheetName as Arguments to this method
 public static void setExcelFile(String Path,String SheetName) throws Exception 
  {
      FileInputStream ExcelFile = new FileInputStream(Path);
      ExcelWBook = new HSSFWorkbook(ExcelFile);
      ExcelWSheet = ExcelWBook.getSheet(SheetName);
     }

 //This method is to read the test data from the Excel cell
 //In this we are passing parameters/arguments as Row Num and Col Num
 public static String getCellData(int RowNum, int ColNum) throws Exception{
 Cell = ExcelWSheet.getRow(RowNum).getCell(ColNum);
 System.out.println(Cell);
    String CellData = Cell.getStringCellValue();
    System.out.println("."+CellData);
    return CellData;
}


}