android 傻瓜式小错误

private void getPersons(){
        String path="content://com.lss.readcontactmassage.PersonDBProvider/query";
        Uri uri = Uri.parse(path);
        ContentResolver contentResolver = getContentResolver();
        Cursor cursor = contentResolver.query(uri, null, null, null, null);

        persons=new ArrayList<Person>();
        if (cursor==null){
            return;
        }
        while (cursor.moveToLast()){
            int id = cursor.getInt(cursor.getColumnIndex("id"));
            String name = cursor.getString(cursor.getColumnIndex("name"));
            String number = cursor.getString(cursor.getColumnIndex("number"));
            Person person = new Person(id, name, number);
            persons.add(person);
        }
        cursor.close();
    }