Null Pointer Exception JSONArray

Question

I'm trying to connect my Android Studio App to a remote database through JSON. When I launch my App it crashes
The Error Logcat is this:

10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: Process: com.example.alessandro.celiachia, PID: 19973 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: java.lang.RuntimeException: An error occured while executing doInBackground() 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at android.os.AsyncTask$3.done(AsyncTask.java:300) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.FutureTask.setException(FutureTask.java:222) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.FutureTask.run(FutureTask.java:242) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.lang.Thread.run(Thread.java:818) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'org.json.JSONArray org.json.JSONObject.getJSONArray(java.lang.String)' on a null object reference 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at com.example.alessandro.celiachia.MarkerJSONParser.parse(MarkerJSONParser.java:23) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at com.example.alessandro.celiachia.MapActivity$ParserTask.doInBackground(MapActivity.java:174) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at com.example.alessandro.celiachia.MapActivity$ParserTask.doInBackground(MapActivity.java:164) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at android.os.AsyncTask$2.call(AsyncTask.java:288) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.FutureTask.run(FutureTask.java:237) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 10-09 11:27:48.166 19973-20495/com.example.alessandro.celiachia E/AndroidRuntime: at java.lang.Thread.run(Thread.java:818)

and the code I use is this:

public class MarkerJSONParser {

static JSONArray jMarkers = null;

/** Receives a JSONObject and returns a list */
public List<HashMap<String,String>> parse(JSONObject jObject){

    try {
        /** Retrieves all the elements in the 'markers' array */
        jMarkers = jObject.getJSONArray("marker");
    } catch (JSONException e) {
        e.printStackTrace();
    }
    /** Invoking getMarkers with the array of json object
     * where each json object represent a marker
     */
    return getMarkers(jMarkers);
}


private List<HashMap<String, String>> getMarkers(JSONArray jMarkers){
    int markersCount = jMarkers.length();
    List<HashMap<String, String>> markersList = new ArrayList<HashMap<String,String>>();
    HashMap<String, String> marker = null;

    /** Taking each marker, parses and adds to list object */
    for(int i=0; i<markersCount;i++){
        try {
            /** Call getMarker with marker JSON object to parse the marker */
            marker = getMarker((JSONObject)jMarkers.get(i));
            markersList.add(marker);
        }catch (JSONException e){
            e.printStackTrace();
        }
    }

    return markersList;
}

/** Parsing the Marker JSON object */
private HashMap<String, String> getMarker(JSONObject jMarker){

    HashMap<String, String> marker = new HashMap<String, String>();
    String lat = "-NA-";
    String lng ="-NA-";


    try {
        // Extracting latitude, if available
        if(!jMarker.isNull("lat")){
            lat = jMarker.getString("lat");
        }

        // Extracting longitude, if available
        if(!jMarker.isNull("lng")){
            lng = jMarker.getString("lng");
        }

        marker.put("lat", lat);
        marker.put("lng", lng);

    } catch (JSONException e) {
        e.printStackTrace();
    }
    return marker;
}
}

I hope some one can help me, I don't understand the error. Thanks a lot