// EFFECTS: returns a list of todo items whose title and/or description
    // contains the search parameter
    // Note: String comparisons are case sensitive
    public List<TodoItem> filterTodoItemsBySearchTerm(String searchString) {
        ArrayList<TodoItem> temp = new ArrayList<TodoItem>();
        for (TodoItem item : todoItems) {
            if (item.getDescription().toLowerCase().contains(searchString.toLowerCase()) || item.getTitle().toLowerCase().contains(searchString.toLowerCase())) {
                temp.add(item);
            }
        }
        return temp;
    }