Android-problem z serializacją

 
private void save(Object o){
		try {
			ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(new File("/sdcard/save_object.bin"))); //Select where you wish to save the file...
			oos.writeObject(o); 
			oos.flush(); 
			oos.close();
		} catch (Exception e) {
			Log.d("asd", e.getMessage());
		}
	}
	private Object load(){
		try {
			ObjectInputStream ois = new ObjectInputStream(new FileInputStream(new File("/sdcard/save_object.bin")));
			Object o = ois.readObject();
			return o;
		} catch (Exception e) {
			Log.d("asd", e.getMessage());
			return null;
		}
	}

Dlaczego ten kod wypluwa NullPointerException?

EDIT: Prawdopodobnie brakowało permission na operacje na SDCard ;)