Getting a very large exception error Java, Eclipse error at line 96

Question

My GUI code

package question1;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.border.TitledBorder;


public class DieGUI extends JFrame{

    private JLabel NumberOfSides;
    private JButton Create, RollDie;
    private JTextField EnterSides;
    private JTextArea History;
    private JPanel optionsPan, diePan, HistoryPan, panel;
    private Die dc;
    private int count = 0;

    public DieGUI() {

        //Label created here
        NumberOfSides = new JLabel("Number of side:");

        //Buttons created here
        Create = new JButton("Create");
        Create.addActionListener(new ListenerObject());

        RollDie = new JButton("Roll Current Die");
        RollDie.addActionListener(new ListenerObject());

        //Text Field for sides created
        EnterSides = new JTextField(15);

        //Text Area for history created
        History = new JTextArea(18,22);
        History.setLineWrap(true);
        History.isEditable();
        History.setBorder(new TitledBorder(null, null, TitledBorder.LEADING, TitledBorder.TOP, null, null) );

        //Creating the left biggest panel
        optionsPan = new JPanel();
        optionsPan.setBorder(BorderFactory.createLineBorder(Color.black));

        //Creating smaller left panel
        diePan = new JPanel();
        diePan.setLayout(new FlowLayout());
        diePan.setBorder(new TitledBorder(null, "New Die", TitledBorder.LEADING, TitledBorder.TOP, null, null) );
        diePan.add(NumberOfSides);
        diePan.add(EnterSides);
        diePan.add(Create);

        //Creating right side panel
        HistoryPan = new JPanel();
        HistoryPan.setBorder(new TitledBorder(null, "Roll History", TitledBorder.LEADING, TitledBorder.TOP, null, null) );
        HistoryPan.setLayout(new FlowLayout());
        HistoryPan.add(History);

        //Creating the full panel
        panel = new JPanel();
        panel.setLayout(new GridLayout(2,1));
        panel.setBorder(new TitledBorder(null, "Dice Options", TitledBorder.LEADING, TitledBorder.TOP, null, null) );

        panel.add(diePan);
        panel.add(RollDie);
        setLayout(new GridLayout(1,2));
        add(panel);
        add(HistoryPan);
        //add(new JScrollPane(History));

    }

    public static void main(String[] args) {

        DieGUI gui = new DieGUI();
        gui.setVisible(true);
        gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        gui.setSize(650,350);
        gui.setTitle("Dice GUI");
        gui.setResizable(false);



    }
    public class ListenerObject implements ActionListener{
        public void actionPerformed(ActionEvent event) {
            try {
                if(event.getSource()== Create) {
                    count=0;
                    History.setText("");
                    String text = EnterSides.getText();
                    int sides = Integer.parseInt(text);
                    Die dc = new Die(sides);
                    History.append("Creating a new die deletes the old one \n \n New Die: "+dc+"\n");
                }
                else if(event.getSource()==RollDie) {
                    dc.roll();
                    int value = dc.getSideUp();
                    count++;
                    History.append("Roll # "+count+" => Value: "+value);
                }
            }
            catch(IllegalArgumentException e) {
                History.append("Die must be either 4,6,10,20 or 100 sided \n");
            }
        }
    }
}

Die class we were given

package question1;

public class Die {

    //data fields
    private int numSides;
    private int sideUp;

    /**
     * Unargumented constructor
     */
    public Die() {
        this(6);
    }

    /**
     * Argumented constructor
     * @param numSides number of sides for the Die
     */
    public Die(int numSides) {
        if(numSides == 4 || numSides == 6 || numSides == 10 || numSides == 20 || numSides == 100)
            this.numSides = numSides;
        else
            throw new IllegalArgumentException("Invalid number of sides.");

        roll();
    }

    /**
     * Copy constructor
     * @param in a Die to copy
     */
    public Die(Die in) {
        this.numSides = in.numSides;
        roll();
    }

    /**
     * Change the value of side up, depends on the number of sides
     */
    public void roll() {
        sideUp = (int)(Math.random()*numSides)+1;
    }

    /**
     * Get the side up (showing)
     * @return side up
     */
    public int getSideUp() { roll(); return sideUp; }

    /**
     * Get the number of sides
     * @return number of sides
     */
    public int getNumSides() { return numSides; }

    /**
     * Standard toString for debugging
     */
    public String toString() { return "Die[" + numSides + ", showing: " + sideUp + "]"; }

    /**
     * Standard equals
     */
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Die other = (Die) obj;
        if (numSides != other.numSides)
            return false;
        if (sideUp != other.sideUp)
            return false;
        return true;
    }



}

Error received

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at question1.DieGUI$ListenerObject.actionPerformed(DieGUI.java:96) at javax.swing.AbstractButton.fireActionPerformed(Unknown Source) at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source) at javax.swing.DefaultButtonModel.setPressed(Unknown Source) at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source) at java.awt.Component.processMouseEvent(Unknown Source) at javax.swing.JComponent.processMouseEvent(Unknown Source) at java.awt.Component.processEvent(Unknown Source) at java.awt.Container.processEvent(Unknown Source) at java.awt.Component.dispatchEventImpl(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source) at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source) at java.awt.Container.dispatchEventImpl(Unknown Source) at java.awt.Window.dispatchEventImpl(Unknown Source) at java.awt.Component.dispatchEvent(Unknown Source) at java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$500(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.awt.EventQueue$4.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue.dispatchEvent(Unknown Source) at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source) at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.pumpEvents(Unknown Source) at java.awt.EventDispatchThread.run(Unknown Source)