exception - java.lang.nullpointerexception attempt to invoke method 'int java.util.List.size()' -

main activity

trying add google map please u can

import java.util.arraylist; import java.util.hashmap; import java.util.list;  import org.json.jsonobject;  import android.app.actionbar; import android.content.intent; import android.graphics.color; import android.os.asynctask; import android.os.bundle; import android.support.v4.app.fragmentactivity; import android.util.log; import android.view.menu; import android.view.menuitem;  import com.google.android.gms.maps.cameraupdatefactory; import com.google.android.gms.maps.googlemap; import com.google.android.gms.maps.supportmapfragment; import com.google.android.gms.maps.model.latlng; import com.google.android.gms.maps.model.markeroptions; import com.google.android.gms.maps.model.polylineoptions; import com.parse.parseanalytics; import com.parse.parseuser;  public class onscreenactivity extends fragmentactivity {      private static final latlng sydney = new latlng(30.8894669, 75.8246729);     private static final latlng connct = new latlng(30.8914863, 75.874398);     googlemap googlemap;     final string tag1 = "pathgooglemapactivity";      public static final string tag = onscreenactivity.class.getsimplename();      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_map);         supportmapfragment fm = (supportmapfragment) getsupportfragmentmanager()                 .findfragmentbyid(r.id.fragment1);         googlemap = fm.getmap();         parseanalytics.trackappopened(getintent());         parseuser currentuser = parseuser.getcurrentuser();         if (currentuser == null) {             navigatetologin();         } else {             log.i(tag, currentuser.getusername());         }         actionbar actionbar = getactionbar();         actionbar.show();         markeroptions options = new markeroptions();         options.position(sydney);         options.position(connct);         googlemap.addmarker(options);         string url = getmapsapidirectionsurl();         readtask downloadtask = new readtask();         downloadtask.execute(url);          googlemap.movecamera(cameraupdatefactory.newlatlngzoom(connct, 16));         addmarkers();      }      private void addmarkers() {         // todo auto-generated method stub         if (googlemap != null) {             googlemap.addmarker(new markeroptions().position(sydney).title(                     "first point"));             googlemap.addmarker(new markeroptions().position(connct).title(                     "second point"));          }      }      private string getmapsapidirectionsurl() {         string waypoints = "waypoints=optimize:true|" + sydney.latitude + ","                 + sydney.longitude + "|" + "|" + connct.latitude + ","                 + connct.longitude;          string sensor = "sensor=false";         string params = waypoints + "&" + sensor;         string output = "json";         string url = "https://maps.googleapis.com/maps/api/directions/"                 + output + "?" + params;         return url;      }      private class readtask extends asynctask<string, void, string> {         @override         protected string doinbackground(string... url) {             string data = "";             try {                 httpconnection http = new httpconnection();                 data = http.readurl(url[0]);             } catch (exception e) {                 log.d("background task", e.tostring());             }             return data;         }          @override         protected void onpostexecute(string result) {             super.onpostexecute(result);             new parsertask().execute(result);         }     }      private class parsertask extends             asynctask<string, integer, list<list<hashmap<string, string>>>> {          @override         protected list<list<hashmap<string, string>>> doinbackground(                 string... jsondata) {              jsonobject jobject;             list<list<hashmap<string, string>>> routes = null;              try {                 jobject = new jsonobject(jsondata[0]);                 pathjsonparser parser = new pathjsonparser();                 routes = parser.parse(jobject);             } catch (exception e) {                 e.printstacktrace();             }             return routes;         }          @override         protected void onpostexecute(list<list<hashmap<string, string>>> routes) {             arraylist<latlng> points = null;             polylineoptions polylineoptions = null;              // traversing through routes             (int = 0; < routes.size(); i++) {                 points = new arraylist<latlng>();                 polylineoptions = new polylineoptions();                 list<hashmap<string, string>> path = routes.get(i);                  (int j = 0; j < path.size(); j++) {                     hashmap<string, string> point = path.get(j);                      double lat = double.parsedouble(point.get("lat"));                     double lng = double.parsedouble(point.get("lng"));                     latlng position = new latlng(lat, lng);                      points.add(position);                 }                  polylineoptions.addall(points);                 polylineoptions.width(2);                 polylineoptions.color(color.blue);             }              googlemap.addpolyline(polylineoptions);         }     }      private void navigatetologin() {         intent intent = new intent(this, login.class);         intent.addflags(intent.flag_activity_new_task);         intent.addflags(intent.flag_activity_clear_task);         startactivity(intent);     }      public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.map, menu);         return true;     }      public boolean onoptionsitemselected(menuitem item) {         int itemid = item.getitemid();         if (itemid == r.id.action_logout) {             parseuser.logout();             navigatetologin();          }         if (itemid == r.id.options) {             intent intent = new intent(this, useroptions.class);             intent.addflags(intent.flag_activity_new_task);             intent.addflags(intent.flag_activity_clear_task);             startactivity(intent);         }         return super.onoptionsitemselected(null);      }  } 

it impossible tell why routes list null in onpostexecute in parsertask, is.

if intended doinbackground in parsertask can return null, should @ least check if routes variable null before attempt it. not fix error , might result in app not doing should, mentioned previously, it's impossible tell more without full log.

if (routes == null) return; suppress error, solve problem if read multiple json files , of them parse.