java.lang.NullPointerException: Attempt to invoke virtual

package com.example.micha.appkillan;

import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.net.Uri;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.view.LayoutInflater;
import android.widget.TextView;

import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.common.api.GoogleApiClient;

import java.util.ArrayList;


public class History extends ActionBarActivity {


    /**
     * ATTENTION: This was auto-generated to implement the App Indexing API.
     * See https://g.co/AppIndexing/AndroidStudio for more information.
     */
    private GoogleApiClient client;
    private ListView listView;



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_history);

        listView = (ListView) findViewById(R.id.listView);
        listView.setAdapter(new VizAdapter(this));
        

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.menu_history, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings) {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @Override
    public void onStart() {
        super.onStart();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        client.connect();
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "History Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app URL is correct.
                Uri.parse("android-app://com.example.micha.appkillan/http/host/path")
        );
        AppIndex.AppIndexApi.start(client, viewAction);
    }

    @Override
    public void onStop() {
        super.onStop();

        // ATTENTION: This was auto-generated to implement the App Indexing API.
        // See https://g.co/AppIndexing/AndroidStudio for more information.
        Action viewAction = Action.newAction(
                Action.TYPE_VIEW, // TODO: choose an action type.
                "History Page", // TODO: Define a title for the content shown.
                // TODO: If you have web page content that matches this app activity's content,
                // make sure this auto-generated web page URL is correct.
                // Otherwise, set the URL to null.
                Uri.parse("http://host/path"),
                // TODO: Make sure this auto-generated app URL is correct.
                Uri.parse("android-app://com.example.micha.appkillan/http/host/path")
        );
        AppIndex.AppIndexApi.end(client, viewAction);
        client.disconnect();
    }
}
class SingleRow{
    String time;
    String date;
    int images;
    SingleRow(String time)
    {
        this.time = time;
       // this.date = date;

    }

}
class VizAdapter extends BaseAdapter{
    private ArrayList<SingleRow> list;
    private Cursor row;
    private DatabaseSQL db;
    private Context context;
    VizAdapter(Context c){
        context = c;
        list = new ArrayList<SingleRow>();
        row = db.listOfHistory();
        int id[] = new int[row.getCount()];
        //System.out.print(row);

        if(row.getCount() > 0)
        {
           row.moveToFirst();
           do {
               String times  =  row.getString(row.getColumnIndex("time"));
             //  String dates  =  row.getString(row.getColumnIndex("date"));
               list.add(new SingleRow(times));
           }
           while(row.moveToNext());
          row.close();
        }

    }

    @Override
    public int getCount() {
        return list.size();
    }

    @Override
    public Object getItem(int position) {
        return list.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View rowList = inflater.inflate(R.layout.history_single_row,parent,false);

        TextView time = (TextView) rowList.findViewById(R.id.textView);

        SingleRow temp = list.get(position);
        time.setText(temp.time);
        return rowList;

    }
}

  
      db.execSQL("CREATE TABLE SUBRUNS ( " +
                        "idSUBRUN INTEGER PRIMARY KEY AUTOINCREMENT, " +
                        "latitude DOUBLE, " +
                        "longitude DOUBLE, " +
                        "time TEXT, " +
                        "date TEXT, " +
                        "high DOUBLE " +
                        "idRUN INT," +
                        "FOREIGN KEY(idRUN) REFERENCES RUN(idRUN)" +
                        ");"
        );
...
       db.execSQL("INSERT INTO SUBRUNS (" +
                "idSUBRUN,latitude, longitude, time, date, high" +
                ")" +
                 "VALUES (" +
                 "1, 20,30,'10:20','01.09.2010', 20"  +
                 ");");
...

public Cursor listOfHistory()
    {    SQLiteDatabase db = this.getReadableDatabase();
        Cursor row = db.rawQuery("SELECT * from SUBRUNS",null);

        return row;
    }