Problem in Realtime data plotting

Question

Hello, i am really new to Visual studio and C# . i was trying to plot the data from the serial port. Its about my final year project, but um messing up everything. here is my code-

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.Windows.Forms.DataVisualization.Charting;
using System.IO.Ports;


namespace Real_time_try1
{
    public partial class Form1 : Form
    {
        // Chart data adding thread
        //private Thread serialPlotter;
        private Thread serialport_thread;
        // Thread Add Data delegate
        
        public delegate void AddDataDelegate();
        public AddDataDelegate addDataDel;


        private DateTime minValue, maxValue;// min and max value for X axis limitation
        public string[] portnames;            //for storing port names
        public int nofport;                //for counting existing no of ports
        
        public Form1()              
        {
            InitializeComponent();
            My_init();

        }
        public void My_init()
        {
                        
            plotstart_but.Enabled = false;
            plotstop_but.Enabled = false;
            connect_but.Enabled = false;
            plotChart.Series["Series1"].ChartType = SeriesChartType.Line;
            plotChart.Series["Series1"].BorderWidth = 1;
            plotChart.Series["Series1"].Color = Color.FromArgb(224, 64, 10);
            plotChart.Series["Series1"].ShadowOffset = 1;
            plotChart.Series["Series1"].XValueType = ChartValueType.DateTime;
            plotChart.Series["Series1"].YValueType = ChartValueType.Double;
                     
        }

        private void Form1_load(object sender, EventArgs e)
        {
            ThreadStart addDataThreadStart = new ThreadStart(AddDataThreadLoop);
            serialport_thread = new Thread(addDataThreadStart);
            addDataDel += new AddDataDelegate(AddData);
            this.plotstart_but_Click(null, EventArgs.Empty);
        }
        private void searchport_but_Click(object sender, EventArgs e)
        {
            portnames = SerialPort.GetPortNames();
            nofport = portnames.Length;
            currentdata_textBox.Text = "search Complete";
            
            if (nofport <= 0)
            {
                MessageBox.Show("Sorry,\nno available \ndata source found ");
                connect_but.Enabled = false;
                return;
            }
            else
            {
                MessageBox.Show("Serial port items found \n Please select the correct device");
                connect_but.Enabled = true;
            }
            for (int i = 0; i < nofport; i++)
            {
                portlist_combo.Items.Add(portnames[i]);
            }
             
        }

        private void connect_but_Click(object sender, EventArgs e)
        {
            plotstart_but.Enabled = true;
            
            
            string sercomname = (String)portlist_combo.SelectedItem;
            try
            {
                serialPort1.PortName = sercomname;
                serialPort1.BaudRate = Convert.ToInt32(baudlist_combo.Text);
                serialPort1.Open();
                MessageBox.Show("Port:" + (String)portlist_combo.SelectedItem + "\nBaudrate:" + (String)baudlist_combo.SelectedItem);
            }
            catch (Exception)
            {
            
            }
            
        }

        private void plotstart_but_Click(object sender, EventArgs e)
        {
            plotstart_but.Enabled = false;
            plotstop_but.Enabled = true;                   
            plotChart.Series.Clear();
            Series newSeries = new Series("SeriesX");
            minValue = DateTime.Now;
            maxValue = minValue.AddSeconds(5);
            plotChart.ChartAreas[0].AxisX.Minimum = minValue.ToOADate();
            plotChart.ChartAreas[0].AxisX.Maximum = maxValue.ToOADate();
            newSeries.ChartType = SeriesChartType.Line;
            newSeries.BorderWidth = 1;
            newSeries.Color = Color.FromArgb(224, 64, 100);
            newSeries.ShadowOffset = 1;
            newSeries.XValueType = ChartValueType.DateTime;
            newSeries.YValueType = ChartValueType.Double;
            plotChart.Series.Add(newSeries);
            //newSeries.AxisLabel="ANKON";
            // start worker threads.
            if (serialport_thread.IsAlive == true)
            {
                serialport_thread.Resume();
            }
            else
            {
                serialport_thread.Start();
            }

        }

        private void plotstop_but_Click(object sender, EventArgs e)
        {

            // Suspend thread
            if (serialport_thread.IsAlive == true)
            {
                serialport_thread.Suspend();
            }

            // Enable all controls on the form
            plotstart_but.Enabled = true;

            // Disable the Stop button
            plotstop_but.Enabled = false;
        }
        
        
        public void AddNewPoint(DateTime timeStamp, Series ptSeries)
        {
            //Series nseries= new Series();
            double rad_val = (double)serialPort1.ReadByte();
            // Add new data point to its series.
            ptSeries.Points.AddXY(timeStamp.ToOADate(), rad_val);

            
            // remove all points from the source series older than 5 seconds.
            double removeBefore = timeStamp.AddSeconds((double)(5) * (-1)).ToOADate();
            if (ptSeries.Points[0].XValue < removeBefore)
            {
                while (ptSeries.Points[0].XValue < removeBefore)
                {
                    ptSeries.Points.RemoveAt(0);
                }
            }

            plotChart.ChartAreas[0].AxisX.Minimum = ptSeries.Points[0].XValue;
            plotChart.ChartAreas[0].AxisX.Maximum = DateTime.FromOADate(ptSeries.Points[0].XValue).AddSeconds(5).ToOADate();
            plotChart.Invalidate();
        }
        
        private void AddDataThreadLoop()
        {
            try
            {
                while (true)
                {
                    // Invoke method must be used to interact with the chart
                    // control on the form!
                    plotChart.Invoke(addDataDel);

                    // Thread is inactive for 200ms
                    Thread.Sleep(200);
                }
            }
            catch
            {
                // Thread is aborted
            }
        }

        public void AddData()
        {
            DateTime timeStamp = DateTime.Now;

            foreach (Series ptSeries in plotChart.Series)
            {
                AddNewPoint(timeStamp, ptSeries);
            }
        }
    }

}

the problem is, i get nothing from it... and null exception arguement from som line is thrown. :( it asks me to assign a new operator to my thread, but i think, i did it in the Load event. Please help... :(