android maps gözükmüyor ...

package com.example.sk_mkacaman.lokasyonproje;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.google.android.gms.maps.CameraUpdateFactory;
import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapView;
import com.google.android.gms.maps.MapsInitializer;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.model.CameraPosition;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.MarkerOptions;


public class FirstFragment extends Fragment implements OnMapReadyCallback{
     GoogleMap mGoogleMap;
    MapView mMapView;
    View mView;
    public FirstFragment() {
        // Required empty public constructor
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        mView= inflater.inflate(R.layout.first_fragment, container, false);
        return mView;
    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);
        mMapView=mView.findViewById(R.id.map);
        if (mMapView!=null){
            mMapView.onCreate(null);
            mMapView.onResume();
            mMapView.getMapAsync(this);
        }

    }


    @Override
    public void onMapReady(GoogleMap googleMap) {
        MapsInitializer.initialize(getContext());

         mGoogleMap = googleMap;
        googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
        googleMap.addMarker(new MarkerOptions().position(new LatLng(41.040694,28.944599)).title("liberty").snippet("mamrama"));
        CameraPosition Liberty = CameraPosition.builder().target(new LatLng(41.040694,28.944599)).zoom(16).bearing(0).tilt(45).build();
        googleMap.moveCamera(CameraUpdateFactory.newCameraPosition(Liberty));

    }
}

Arkadaşlar böyle bir fragment kullanıyorum. Harita ekranda gözükmüyor. Sol altta google simgesi gözüküyor fakat harita gelmiyor. Sebebi ne olabilir ?