Fehler beim Einbinden von Google Maps in eine App

import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v4.app.FragmentManager;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.OnMapReadyCallback;
import com.google.android.gms.maps.SupportMapFragment;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener, OnMapReadyCallback {

    SupportMapFragment sMapFragment;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        sMapFragment = SupportMapFragment.newInstance();


        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);
        sMapFragment.getMapAsync(this);
    }

    @Override
    public void onBackPressed() {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START)) {
            drawer.closeDrawer(GravityCompat.START);
        } else {
            super.onBackPressed();
        }
    }




    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item) {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_map) {
            // Handle the camera action
            map map = new map();
            FragmentManager manager = getSupportFragmentManager();
            manager.beginTransaction().replace(R.id.relativelayout_for_fragment, map).commit();
        } else if (id == R.id.nav_location) {
            location_fragment location = new location_fragment();
            FragmentManager manager = getSupportFragmentManager();
            manager.beginTransaction().replace(R.id.relativelayout_for_fragment, location).commit();

        } else if (id == R.id.nav_events) {
            new_event_fragment events= new new_event_fragment();
            FragmentManager manager = getSupportFragmentManager();
            manager.beginTransaction().replace(R.id.relativelayout_for_fragment, events).commit();

        } else if (id == R.id.nav_calendar) {
            kalender_fragment kalendar = new kalender_fragment();
            FragmentManager manager = getSupportFragmentManager();
            manager.beginTransaction().replace(R.id.relativelayout_for_fragment, kalendar).commit();

        } else if (id == R.id.nav_chat) {

            chat_fragment chat =  new chat_fragment();
            FragmentManager manager = getSupportFragmentManager();
            manager.beginTransaction().replace(R.id.relativelayout_for_fragment, chat).commit();

        }
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }

    @Override
    public void onMapReady(GoogleMap googleMap) {

    }
}

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

import com.google.android.gms.maps.GoogleMap;
import com.google.android.gms.maps.MapFragment;
import com.google.android.gms.maps.OnMapReadyCallback;

import static de.androidnewcomer.partypeople.R.layout.fragment_gmaps;


/**
 * A simple {@link Fragment} subclass.
 */
public class map extends Fragment implements OnMapReadyCallback {

    @Nullable



    public View onViewCreated(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(fragment_gmaps, container, false);

    }

    @Override
    public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        MapFragment fragment = (MapFragment)getChildFragmentManager().findFragmentById(R.id.map);
        fragment.getMapAsync(this);

    }






    @Override
    public void onMapReady(GoogleMap googleMap) {

    }
}