Edit Friends not showing anything

public static final String TAG = EditFriendsActivity.class.getSimpleName();

protected List<ParseUser> mUsers;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_edit_friends);
}

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

    ParseQuery query = ParseUser.getQuery();
    query.orderByAscending(ParseConstants.KEY_USERNAME);
    // Add search feature later. Look at the Parse documentation regarding this section
    query.setLimit(1000);
    query.findInBackground(new FindCallback() {
        @Override
        public void done(List users, ParseException e) {
            if (e == null) {
                // Success
                mUsers = users;
                String[] usernames = new String[mUsers.size()];
                int i = 0;
                for (ParseUser user : mUsers) {
                    usernames[i] = user.getUsername();
                    i++;
                }
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                        EditFriendsActivity.this,
                        android.R.layout.simple_list_item_checked,
                        usernames);
                setListAdapter(adapter);

            } else {
                Log.e(TAG, e.getMessage());
                AlertDialog.Builder builder = new AlertDialog.Builder(EditFriendsActivity.this);
                builder.setMessage(e.getMessage())
                        .setTitle(R.string.error_title)
                        .setPositiveButton(android.R.string.ok, null);
                AlertDialog dialog = builder.create();
                dialog.show();
            }
        }

        @Override
        public void done(Object o, Throwable throwable) {

        }
    });
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_edit_friends, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
        return true;
    }

    return super.onOptionsItemSelected(item);
}

<ListView
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@android:id/list"
    android:layout_alignParentTop="true"
    android:layout_alignParentLeft="true"
    android:layout_alignParentStart="true"/>