Error using Android next map map library.

public class MainActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener, MapView.MapViewEventListener, MapView.POIItemEventListener {

    Public static final string API_KEY = "Next Map API"; //Actually use the following API key: I'll cover it here

    private BackPressCloseHandler backPressCloseHandler;
    private MapView mapView;
    MapPoint.GeoCoordinate CurrentLocation;
    MapPOIItem mDefaultMarker;


    public static final int FINE_PERMISSION = 1000;

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

        mapView = new MapView(this);
        mapView.setDaumMapApiKey(API_KEY);
        ViewGroup mapViewContainer = (ViewGroup)findViewById(R.id.container);
        mapViewContainer.addView(mapView);

        int permissionFine = ContextCompat.checkSelfPermission(this, Manifest.permission.ACCESS_FINE_LOCATION); // Location Permission Variable
        checkGPSPermission(permissionFine);

        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick (View view) {
               mapView.setCurrentLocationTrackingMode(MapView.CurrentLocationTrackingMode.TrackingModeOnWithoutHeading); //Get Current Location
            }
        });

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        backPressCloseHandler = newBackPressCloseHandler (this); //Handler to exit by pressing the Back key twice
        CreateDefaultMarker (mapView); // Error when calling this part


    }

    private void createDefaultMarker(MapView mapView) {
        mDefaultMarker = new MapPOIItem();
        mDefaultMarker.setItemName("Marker");
        mDefaultMarker.setTag(0);
        mDefaultMarker.setMapPoint(MapPoint.mapPointWithGeoCoord(126.8439946101, 37.3282802259));
        mDefaultMarker.setMarkerType(MapPOIItem.MarkerType.BluePin);
        mDefaultMarker.setSelectedMarkerType(MapPOIItem.MarkerType.RedPin);

        mapView.addPOIItem(mDefaultMarker);
        mapView.selectPOIItem(mDefaultMarker, true);
        mapView.setMapCenterPoint(MapPoint.mapPointWithGeoCoord(126.8439946101, 37.3282802259), true);
    }
    //Omit the rest (bottom part)