Tengo este ejemplo de código para copiar archivos y directorios de una ubicación a otra. Pero esta excepción sigue apareciendo cada vez que ejecuto el programa. ¿Alguien puede ayudarme a encontrar el error?

Excepción en el hilo "principal" java.lang.NullPointerException

 public void listFilesAndFilesSubDirectories(String directoryName) throws FileNotFoundException, IOException { File directory = new File(directoryName); //get all the files from a directory File[] fList = directory.listFiles(); for (File file : fList) { if (file.isFile()) { //System.out.println(file.getAbsolutePath()); System.out.println("File"); File source = new File("C:\\Users\\Core i3\\Desktop\\Check me\\" + file); File dest = new File("C:\\Users\\Core i3\\Desktop\\New folder"); System.out.println(source); InputStream is = null; OutputStream os = null; try { is = new FileInputStream(source); os = new FileOutputStream(dest); byte[] buffer = new byte[1024]; int length; while ((length = is.read(buffer)) > 0) { os.write(buffer, 0, length); } } finally { is.close(); os.close(); } } else if (file.isDirectory()) { listFilesAndFilesSubDirectories(file.getAbsolutePath()); System.out.println("Directory"); File source = new File("C:\\Users\\Core i3\\Desktop\\Check me\\" + file); File dest = new File("C:\\Users\\Core i3\\Desktop\\New folder"); InputStream is = null; OutputStream os = null; try { is = new FileInputStream(source); os = new FileOutputStream(dest); byte[] buffer = new byte[1024]; int length; while ((length = is.read(buffer)) > 0) { os.write(buffer, 0, length); } } finally { is.close(); os.close(); } } } }