throw new IllegalArgumentException("value to key is not an arraylist");
throw new IllegalArgumentException("value to key is not an arraylist, the value class is: " + get(key).getClass().getName());
    public ArrayList getArrayList(Object key) {        try {            return (ArrayList) get(key);        } catch (ClassCastException e) {            throw new IllegalArgumentException("value to key is not an arraylist");        }    }