Need a help in appactivity crash issue My code is:

package wallet.ask.com.abcd;
import android.app.ProgressDialog;
import android.graphics.Color;
import android.os.AsyncTask;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import com.github.mikephil.charting.charts.BarChart;
import com.github.mikephil.charting.data.BarData;
import com.github.mikephil.charting.data.BarDataSet;
import com.github.mikephil.charting.data.BarEntry;
import com.github.mikephil.charting.utils.ColorTemplate;
import org.json.JSONArray;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
String[] stringArray1, stringArray2;
ArrayList<String> arrayListString1, arrayListString2;
List<ChartPojo> list;
 ChartPojo object;
ArrayList<BarEntry> valueSet1 = new ArrayList<>();
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        list = new ArrayList<ChartPojo>();

        new LoadDataAsyncTask().execute();

        arrayListString1 = new ArrayList<String>();
        arrayListString2 = new ArrayList<String>();

        stringArray1 = new String[arrayListString1.size()];
        stringArray2 = new String[arrayListString2.size()];


        BarChart chart = (BarChart) findViewById(R.id.chart);
BarData data = new BarData(arrayListString1, getDataSet());

        chart.setData(data);
        chart.setDescription("My Chart");
        chart.animateXY(2000, 2000);
        chart.invalidate();

    }
 private ArrayList<BarDataSet> getDataSet() {
        ArrayList<BarDataSet> dataSets = null;

BarEntry v1e1 = new BarEntry(new float[stringArray2.length], stringArray1.length); // Jan
        valueSet1.add(v1e1);

BarDataSet barDataSet1 = new BarDataSet(valueSet1, "Brand 1");
        barDataSet1.setColor(Color.rgb(0, 155, 0));

        dataSets = new ArrayList<>();
        dataSets.add(barDataSet1);
        return dataSets;
}
private ArrayList<String> getXAxisValues() {
        ArrayList<String> xAxis = new ArrayList<>();
        xAxis.add("JAN");
        xAxis.add("FEB");
        xAxis.add("MAR");
        xAxis.add("APR");
        xAxis.add("MAY");
        xAxis.add("JUN");
        return xAxis;
    }
class LoadDataAsyncTask extends AsyncTask<String, String, String> {
        private ProgressDialog dialog;
        String response = "";
        private JSONObject res;
        String runtime;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            dialog = new ProgressDialog(MainActivity.this);
            dialog.setMessage("Please Wait..");
            dialog.setCancelable(false);
            dialog.show();
        }

        @Override
        protected String doInBackground(String... params) {
            try {

                JSONObject vehicle_json = new JSONObject();

                vehicle_json.put("pAccountId", "2");
                vehicle_json.put("unitId", "160323132");
                vehicle_json.put("startDate", "2017-07-22 11:23:12");
                vehicle_json.put("endDate", "2017-07-29 11:23:12");
                //  vehicle_json.put("minSpeed",speed);
//                Log.d("stopstop123456", AccountId + " " + unitId + " " + fromDate + toDate);


                res = CustomHttpClient.postJsonObject("http://", vehicle_json, MainActivity.this);


                String resData = res.getString("ResponseData");
                Log.d("stopstop12345", resData);
//                JSONObject jres = new JSONObject(resData);

                JSONArray array1 = new JSONArray(resData);
                //JSONArray array=new JSONArray(array1.get(0).toString());
                //JSONObject jobj=array1.get(0);
                JSONArray array = new JSONArray(array1.get(0).toString());

                for (int i = 0; i < array.length(); i++) {
                    JSONObject jsonVehicleObj = new JSONObject(array.get(i).toString());

                    ChartPojo p = new ChartPojo();

                    p.setStrDate(jsonVehicleObj.getString("date"));
                    p.setStrDistance(jsonVehicleObj.getString("distance"));
                    p.setStrRunTime(jsonVehicleObj.getString("run_time"));

                    list.add(p);
}

            } catch (Exception e) {
                Log.d("errorrrr", e.toString());
            }
for (int j = 0; j < list.size(); j++) {

                object = list.get(j);
arrayListString1.add(object.getStrDate());
 stringArray2 = arrayListString1.toArray(stringArray1);

   arrayListString2.add(object.getStrRunTime());
   stringArray2 = arrayListString2.toArray(stringArray2);
}
            return response;
        }

        @Override
        protected void onPostExecute(String s) {
            super.onPostExecute(s);
            if (dialog.isShowing()) {
                dialog.dismiss();
            }}
    }}