How to get rid of the java error.lang.NullPointerException?

The bottom line is this

ArrayList<eventcalendar> event_calendar_list = null;
 for (int i = 0; i < tvSeries.size(); i++) {
System.out.println(tvSeries.get(i).getKinopoiskID());

 ArrayList<series> series = null;
 try {
 series = ld.loadMyMuviCalendar(tvSeries.get(i).getKinopoiskID().toString());
 } catch (IOException e) {
e.printStackTrace();
 } catch (JSONException e) {
e.printStackTrace();
}

 for (int ii = 0; ii < series.size(); ii++) {
 Ec EventCalendar = new EventCalendar();
ec.setDate(series.get(ii).getDate());
ec.setMuvi_obj(tvSeries.get(i));
ec.setSeri_obj(series.get(ii));
System.out.println(ec);
//
event_calendar_list.add(ec);
 }</series></eventcalendar>

The data all come and run through the array goes as it should, even can display these data in console but when trying to add them in event_calendar_list gives an error java.lang.NullPointerException