Ribbit app force closes after Signup

    package com.davidwestberry.ribbit.ui;

    import android.app.AlertDialog;
    import android.os.Bundle;
    import android.support.v4.app.Fragment;
    import android.util.Log;
    import android.view.ContextMenu;
    import android.view.LayoutInflater;
    import android.view.MenuInflater;
    import android.view.MenuItem;
    import android.view.View;
    import android.view.ViewGroup;
    import android.widget.AdapterView;
    import android.widget.GridView;
    import android.widget.TextView;

    import com.davidwestberry.ribbit.R;
    import com.davidwestberry.ribbit.adapters.UserAdapter;
    import com.davidwestberry.ribbit.utils.ParseConstants;
    import com.parse.FindCallback;
    import com.parse.ParseException;
    import com.parse.ParseQuery;
    import com.parse.ParseRelation;
    import com.parse.ParseUser;
    import com.parse.SaveCallback;

    import java.util.List;

    public class FriendsFragment extends Fragment {

        private static final String TAG =     FriendsFragment.class.getSimpleName();

        protected List<ParseUser> mFriends;
        protected ParseRelation<ParseUser> mFriendsRelation;
        protected ParseUser mCurrentUser;
        protected GridView mGridView;

        /**
         * Mandatory empty constructor for the fragment manager to     instantiate the
         * fragment (e.g. upon screen orientation changes).
         */
        public FriendsFragment() {
        }

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

            mGridView = (GridView) rootview.findViewById(R.id.friendsGrid);

            TextView emptyTextView = (TextView) rootview.findViewById(android.R.id.empty);
            mGridView.setEmptyView(emptyTextView);

            registerForContextMenu(rootview);

            return rootview;
        }

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

            mCurrentUser = ParseUser.getCurrentUser();
            mFriendsRelation = mCurrentUser.getRelation(ParseConstants.KEY_FRIENDS_RELATION);
            if (!mCurrentUser.isNew()) {
                getFriendsList();
            }
            /**
             * This interface must be implemented by activities that contain     this
             * fragment to allow an interaction in this fragment to be     communicated
             * to the activity and potentially other fragments contained in that
             * activity.
             * <p/>
             * See the Android Training lesson <a href=
             *     "http://developer.android.com/training/basics/fragments/communicatin    g.html"
             * >Communicating with Other Fragments</a> for more information.
             */
        }

        private void getFriendsList() {
            ParseQuery<ParseUser> query = mFriendsRelation.getQuery();
            query.addAscendingOrder(ParseConstants.KEY_USERNAME);
            query.findInBackground(new FindCallback<ParseUser>() {
                @Override
                public void done(List<ParseUser> friends, ParseException e) {
                    mFriends = friends;

                    int i = 0;
                    if (e == null) {
                        String[] usernames = new String[mFriends.size()];
                        for (ParseUser user : mFriends) {
                            usernames[i] = user.getUsername();
                            i++;
                        }
                        if (mGridView.getAdapter() == null) {
                            UserAdapter adapter = new UserAdapter(getActivity(),    mFriends);
                            mGridView.setAdapter(adapter);
                        }
                        else{
                             ((UserAdapter)mGridView.getAdapter()).refill(mFriends);
                        }
                    } else {
                        Log.e(TAG, e.getMessage());
                        Log.i(TAG, "Username: " + mCurrentUser.getUsername());
                        Log.i(TAG, "Authenticated: " +  mCurrentUser.isAuthenticated());
                        Log.i(TAG, "Data Available: " +    mCurrentUser.isDataAvailable());
                    }
                }
            });
        }

        private void ErrorAlert(String title, String message) {
            AlertDialog.Builder builder = new     AlertDialog.Builder(getActivity());
            builder.setMessage(message)
                    .setTitle(title)
                    .setPositiveButton(android.R.string.ok, null);
            AlertDialog dialog = builder.create();
            dialog.show();
        }

        @Override
        public void onCreateContextMenu(ContextMenu menu, View v,   ContextMenu.ContextMenuInfo menuInfo) {
            super.onCreateContextMenu(menu, v, menuInfo);

            AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo) menuInfo;
            menu.setHeaderTitle(mFriends.get(info.position).getUsername());
            MenuInflater inflater = getActivity().getMenuInflater();
            inflater.inflate(R.menu.menu_friends_list, menu);
        }

        @Override
        public boolean onContextItemSelected(MenuItem item) {
            AdapterView.AdapterContextMenuInfo menuInfo = (AdapterView.AdapterContextMenuInfo) item.getMenuInfo();
            int selectId = item.getItemId();
            int selectPosition = menuInfo.position;
            if (selectId == R.id.action_remove) {
                Log.i(TAG, mFriends.get(selectPosition).getUsername());
                mFriendsRelation.remove(mFriends.get(selectPosition));
                mCurrentUser.saveInBackground(new SaveCallback() {
                    @Override
                    public void done(ParseException e) {
                        if (e != null) {
                            Log.e(TAG, e.getMessage());
                        }
                    }
                });
            }
            getFriendsList();
            return super.onContextItemSelected(item);
        }
    }