求问此段代码有何问题？

C# code

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Text;using System.Windows.Forms;using System.Collections;namespace HaveATry{    public partial class Form1 : Form    {        ArrayList points;        Point currentPoint;        Pen thepen;        float penwidth;        SolidBrush thebrush;        Color thecolor;        public Form1()        {            InitializeComponent();        }        private void Form1_Paint(object sender, PaintEventArgs e)        {            Graphics g = e.Graphics;            Point[] ps=(Point[])points.ToArray(typeof(Point));            if (radioButton1.Checked)                g.DrawLine(Pens.Black, ps[0], ps[ps.Length - 1]);            else if (radioButton2.Checked)                g.DrawRectangle(thepen, ps[0].X, ps[0].Y, ps[ps.Length - 1].X - ps[0].X, ps[ps.Length - 1].Y - ps[0].Y);        }        private void Form1_MouseUp(object sender, MouseEventArgs e)        {            if (currentPoint.X != e.X || currentPoint.Y != e.Y)            {                currentPoint.X = e.X;                currentPoint.Y = e.Y;                points.Add(currentPoint);                this.Invalidate();                this.Update();            }        }    }}

报错的是这一行
Point[] ps=(Point[])points.ToArray(typeof(Point));
说：未将对象引用设置到对象的实例
求问应该如何处理？

[解决办法]
points压根没有赋值过嘛！在构造函数里加上：

points = new ArrayList();
[解决办法]
ArrayList points;
Point currentPoint;
Pen thepen;
float penwidth;
SolidBrush thebrush;
Color thecolor;

你都没有初始化值！！——即使你初始化了默认值，你根本就没有地方赋值！！
你获取一个空数据，空集合 为了什么？？