java - 当我按导航栏中的与我们联系时，我的应用程序停止工作

public class ContactUsFragment extends FragmentActivity implements OnMapReadyCallback { private GoogleMap mMap; public static ContactUsFragment newInstance(){ ContactUsFragment fragment = new ContactUsFragment(); return fragment; } public ContactUsFragment() { } @BindView(R.id.contact_us_root) LinearLayout root; public View onCreateView(final LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { final View rootView = inflater.inflate(R.layout.fragment_contact_us, container, false); ButterKnife.bind(this, rootView); TextView textView1 = (TextView)findViewById(R.id.t1); TextView textView2 = (TextView)findViewById(R.id.t2); TextView textView3 = (TextView)findViewById(R.id.t3); TextView textView4 = (TextView)findViewById(R.id.t4); TextView textView5 = (TextView)findViewById(R.id.t5); TextView textView6 = (TextView)findViewById(R.id.t6); ImageView imageView = (ImageView)findViewById(R.id.ib1); imageView.setImageResource(R.drawable.fb1); ImageView imageView1 = (ImageView)findViewById(R.id.ib2); imageView1.setImageResource(R.drawable.gp1); ImageView imageView2 = (ImageView)findViewById(R.id.ib3); imageView2.setImageResource(R.drawable.pin1); ImageView imageView3 = (ImageView)findViewById(R.id.ib4); imageView3.setImageResource(R.drawable.add); ImageView imageView4 = (ImageView)findViewById(R.id.ib5); imageView4.setImageResource(R.drawable.phone); ImageView imageView5 = (ImageView)findViewById(R.id.ib6); imageView5.setImageResource(R.drawable.gmail); SupportMapFragment mapFragment = (SupportMapFragment) getSupportFragmentManager() .findFragmentById(R.id.map); mapFragment.getMapAsync(this); return rootView; } @Override public void onMapReady(GoogleMap googleMap) { mMap = googleMap; LatLng loc = new LatLng(12.77, 77.52); mMap.addMarker(new MarkerOptions().position(loc).title("Student Zone")); mMap.moveCamera(CameraUpdateFactory.newLatLng(loc)); }} 01-18 14:12:04.827 30314-30314/in.astudentzone.studentzone E/UncaughtException: java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:418) at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:457) at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:449) at in.astudentzone.studentzone.activities.Home.selectDrawerItem(Home.java:133) at in.astudentzone.studentzone.activities.Home$1.onNavigationItemSelected(Home.java:66) at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:152) at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:810) at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152) at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:957) at android.support.design.internal.NavigationMenuPresenter$1.onClick(NavigationMenuPresenter.java:318) at android.view.View.performClick(View.java:4789) at android.view.View$PerformClick.run(View.java:19881) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5292) 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:904) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699) 01-18 14:12:04.831 30314-30380/in.astudentzone.studentzone D/FA: Logging event (FE): _ae, Bundle[{_o=crash, _sc=Home, _si=3096521095531764912, timestamp=1484728924827, fatal=1}] 01-18 14:12:05.090 30314-30314/in.astudentzone.studentzone E/AndroidRuntime: FATAL EXCEPTION: main Process: in.astudentzone.studentzone, PID: 30314 java.lang.NullPointerException: Attempt to write to field 'android.support.v4.app.FragmentManagerImpl android.support.v4.app.Fragment.mFragmentManager' on a null object reference at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:418) at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:457) at android.support.v4.app.BackStackRecord.replace(BackStackRecord.java:449) at in.astudentzone.studentzone.activities.Home.selectDrawerItem(Home.java:133) at in.astudentzone.studentzone.activities.Home$1.onNavigationItemSelected(Home.java:66) at android.support.design.widget.NavigationView$1.onMenuItemSelected(NavigationView.java:152) at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:810) at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:152) at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:957) at android.support.design.internal.NavigationMenuPresenter$1.onClick(NavigationMenuPresenter.java:318) at android.view.View.performClick(View.java:4789) at android.view.View$PerformClick.run(View.java:19881) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5292) 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:904) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:699) 01-18 14:12:06.574 30314-30314/in.astudentzone.studentzone I/Process: Sending signal. PID: 30314 SIG: 9