GPS on Android - Map = null

I'm making an app for people with addresses. Every time I open the map by setting the initial location with the cell phone's GPS, the app hangs and closes.

[UPDATE] In analysis to the code I noticed that the variable "map" is receiving null value, causing hard close in the application. I need help identifying the error.

Follow the 4 classes:

public class MapaFragment extends SupportMapFragment {

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

    FragmentActivity context = getActivity();

    AlunoDAO dao = new AlunoDAO(context);
    List<Aluno> alunos = dao.getLista();
    for (Aluno aluno : alunos) {

        GoogleMap map = getMap();

        Localizador localizador = new Localizador(context);
        LatLng localAluno = localizador.getCoordenada(aluno.getRua() + "," + aluno.getNumero() + "-" + aluno.getBairro() + "," + aluno.getCidade());

        if (localAluno != null) {
            MarkerOptions options = new MarkerOptions().title(aluno.getNome()).position(localAluno);
            map.addMarker(options);
        }
    }
    dao.close();
}

public void centralizaNo(LatLng local) {
    GoogleMap map = getMap();
    CameraUpdate update = CameraUpdateFactory.newLatLngZoom(local , 15);
    map.animateCamera(update );
}
}

Finder:

public class Localizador {

private Context context;

public Localizador(Context context){
    this.context = context;
}

public LatLng getCoordenada(String endereco) {
    Geocoder geocoder = new Geocoder(context);

    try {
        List<Address> enderecos = geocoder.getFromLocationName(endereco, 1);
        if (!enderecos.isEmpty()){
            Address enderecoLocalizado = enderecos.get(0);
            double latitude = enderecoLocalizado.getLatitude();
            double longitude = enderecoLocalizado.getLongitude();

            return new LatLng(latitude, longitude);
        } else {
            return null;
        }
    } catch (IOException e) {
        return null;
    }
}
}

Show nearby students:

public class MostraAlunosProximos extends FragmentActivity{

private AtualizadorDePosicao atualizador;

@Override
protected void onCreate(Bundle arg0) {
    super.onCreate(arg0);
    setContentView(R.layout.map_layout);

    FragmentManager manager = getSupportFragmentManager();

    FragmentTransaction transaction = manager.beginTransaction();

    MapaFragment mapaFragment = new MapaFragment();
    transaction.replace(R.id.mapa, new MapaFragment());
    transaction.commit();

    atualizador = new AtualizadorDePosicao(this, mapaFragment);

}

@Override
protected void onDestroy() {
    super.onDestroy();

    atualizador.cancelar();
}
}

Position updater:

public class AtualizadorDePosicao implements LocationListener {

private LocationManager locationManager;
private MapaFragment mapa;

public AtualizadorDePosicao(Activity activity, MapaFragment mapa) {
    this.mapa = mapa;

    locationManager = (LocationManager) activity.getSystemService(Context.LOCATION_SERVICE);

    String provider = LocationManager.GPS_PROVIDER;
    long tempoMinimo = 0;
    float distanciaMinima = 0;

    locationManager.requestLocationUpdates(provider, tempoMinimo, distanciaMinima, this);
}

public void cancelar() {
    locationManager.removeUpdates(this);
}

@Override
public void onLocationChanged(Location novaLocalizacao) {
    double latitude = novaLocalizacao.getLatitude();
    double longitude = novaLocalizacao.getLongitude();

    LatLng local = new LatLng(latitude, longitude);

    mapa.centralizaNo(local);
}

@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}

@Override
public void onProviderEnabled(String provider) {
}

@Override
public void onProviderDisabled(String provider) {
}
}

[UPDATE] Logcat error trying to open map:

05-20 16:23:34.893  15954-15954/cadastro.grupotmt.com.br.cadastrotmt E/SysUtils﹕ ApplicationContext is null in ApplicationStatus
05-20 16:23:40.276  15954-15954/cadastro.grupotmt.com.br.cadastrotmt E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: cadastro.grupotmt.com.br.cadastrotmt, PID: 15954
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.gms.maps.GoogleMap.animateCamera(com.google.android.gms.maps.CameraUpdate)' on a null object reference
        at cadastro.grupotmt.com.br.cadastrotmt.MapaFragment.centralizaNo(MapaFragment.java:46)
        at cadastro.grupotmt.com.br.cadastrotmt.AtualizadorDePosicao.onLocationChanged(AtualizadorDePosicao.java:43)
        at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:281)
        at android.location.LocationManager$ListenerTransport.access$000(LocationManager.java:210)
        at android.location.LocationManager$ListenerTransport$1.handleMessage(LocationManager.java:226)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5312)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:901)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:696)