Exception in thread "AWT-EventQueue-0"

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at java.awt.Container.addImpl(Unknown Source)
        at java.awt.Container.add(Unknown Source)
        at javax.swing.JFrame.addImpl(Unknown Source)
        at java.awt.Container.add(Unknown Source)
        at InterfaceGUI.<init>(InterfaceGUI.java:12)
        at Interface.lambda$main$0(Interface.java:31)
        at java.awt.event.InvocationEvent.dispatch(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.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)

import javax.swing.*;
 
public class Interface  {
    public static int count = 0;
    static class Student{
 
        String Surname;
        int Course;
        boolean Debt;
 
        Student(String surname, int course, boolean debt) {
            Surname = surname;
            Course = course;
            Debt = debt;
        }
 
        int getDebts(int course){
            if((Course == course) && (Debt)){
                count++;
            }
            return count;
        }
    }
 
 
    public static void main(String[] args) throws ClassNotFoundException, UnsupportedLookAndFeelException, InstantiationException, IllegalAccessException {
 
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
 
        SwingUtilities.invokeLater(() -> {
            InterfaceGUI frame = new InterfaceGUI();
            frame.setVisible(true);
        });
 
    }
 
}

import javax.swing.*;
import java.awt.event.*;
import java.awt.*;
 
public class InterfaceGUI extends JFrame {
    private JTextField debtTextIn;
    private JButton debtBtn;
    private JPanel rootPanel;
    private JTextField debtTextOut;
 
    InterfaceGUI(){
        add(rootPanel);
 
        setTitle("Student Form");
        setSize(400, 200);
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        debtBtn.addActionListener(e -> {
            Interface.count = 0;
            Interface.Student [] Students = new Interface.Student[5];
            Students[0] = new Interface.Student("Smith" , 1, true);
            Students[1] = new Interface.Student("Legend" , 2, false);
            Students[2] = new Interface.Student("Bold" , 1, true);
            Students[3] = new Interface.Student("Jack" , 2, true);
            Students[4] = new Interface.Student("Dude" , 1, true);
            String OutInfo = null;
            for (Interface.Student Student : Students) {
                int textFieldValue = Integer.parseInt(debtTextIn.getText());
                OutInfo = Integer.toString(Student.getDebts(textFieldValue));
            }
            debtTextOut.setText(OutInfo);
        });
 
    }
}