First of all, I apologize for my bad english, it's not my primary language. 
I'm having a problem with my code when it's reading an excel file (xlsx). The first time I used my code it works perfectly, but now I can't use it. 
The excel content is printed on the console, but next to it there is a NullPointerException that is caused by the for loop marked with the (-->>>). 
If anyone can help me, I would be very thankful, this code has given me several headaches. 

```
package modleerjava;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import org.apache.poi.ss.usermodel.Workbook;
import org.apache.poi.ss.usermodel.Row;
import org.apache.poi.ss.usermodel.Sheet;
import org.apache.poi.xssf.usermodel.XSSFWorkbook;

public class leerExcel {
public void readExcel(String rutaFile,String nombreFile, String sheetName ) 
 throws IOException {
    File file = new File ("C:/Users/Pablo/Desktop/prueba.xlsx"); 
    FileInputStream inputStream = new FileInputStream(file);  
    XSSFWorkbook excelWorkbook ; 
    excelWorkbook = new XSSFWorkbook(inputStream);
    Sheet excelSheet = excelWorkbook.getSheet(sheetName); 
    int filasCount = excelSheet.getLastRowNum()-excelSheet.getFirstRowNum(); 

    for (int i=0; i< filasCount+1 ; i++) { 
        Row filas;
        filas = excelSheet.getRow(i);

 -->>>  for (int j=0 ; j < filas.getLastCellNum(); j++) { 
            System.out.print(filas.getCell(j).getStringCellValue()+"|| ");
        }
        System.out.println();
    }       

}

}

```