java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()

Hi!

I'm having this error when i run the app. when i run it in debug mode i figured out that the variable usernames is returned as null and i really don't know how to fix the problem. I saw the teacher's code and the files are almost identical.

By the way, mMessages is returning values, so, usernames should be populate with the values too.

Any help?

This is the InboxFragment class:

public class InboxFragment extends ListFragment {

protected List<ParseObject> mMessages;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_inbox, container, false);

    return rootView;
}

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

    //We create a Query object to get the messages for this User
    ParseQuery<ParseObject> query = new ParseQuery<ParseObject>(ParseConstants.CLASS_MESSAGES);
    //We filter the messages just for the current user logged in the app
    query.whereEqualTo(ParseConstants.KEY_RECIPIENT_IDS, ParseUser.getCurrentUser().getObjectId());
    query.addDescendingOrder(ParseConstants.KEY_CREATED_AT);
    query.findInBackground(new FindCallback<ParseObject>() {
        @Override
        public void done(List<ParseObject> messages, ParseException e) {

            if (e == null) {
                //We got messages
                mMessages = messages;

                String[] usernames = new String[mMessages.size()];

                int i = 0;
                for (ParseObject message : mMessages) {
                    usernames[i] = message.getString(ParseConstants.KEY_SENDER_NAME);
                    i++;
                }

                //Sets the Adapter to our layout as a checkbox type
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                        getListView().getContext(),
                        android.R.layout.simple_list_item_1,
                        usernames);
                setListAdapter(adapter);
            }
        }
    });

}

}

And this is the error i'm getting:

06-27 09:27:04.175 3060-3060/com.example.pmercedes.ribbit E/AndroidRuntime﹕ FATAL EXCEPTION: main Process: com.example.pmercedes.ribbit, PID: 3060 java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394) at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362) at android.widget.AbsListView.obtainView(AbsListView.java:2344) at android.widget.ListView.makeAndAddView(ListView.java:1864) at android.widget.ListView.fillDown(ListView.java:698) at android.widget.ListView.fillFromTop(ListView.java:759) at android.widget.ListView.layoutChildren(ListView.java:1673) at android.widget.AbsListView.onLayout(AbsListView.java:2148) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.widget.RelativeLayout.onLayout(RelativeLayout.java:1076) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1626) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573) at android.widget.FrameLayout.onLayout(FrameLayout.java:508) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.support.v7.internal.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:493) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573) at android.widget.FrameLayout.onLayout(FrameLayout.java:508) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1703) at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1557) at android.widget.LinearLayout.onLayout(LinearLayout.java:1466) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:573) at android.widget.FrameLayout.onLayout(FrameLayout.java:508) at android.view.View.layout(View.java:15596) at android.view.ViewGroup.layout(ViewGroup.java:4966) at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2072) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1829) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767) at android.view.Choreographer.doCallbacks(Choreographer.java:580) at android.view.Choreographer.doFrame(Choreographer.java:550) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753) at android.os.Handler.handleCallback(Handler.java:739) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5221) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)

Someone with the same problem?