Date Must not be null

I want to use the DateChooser in my application. I have already installed and implemented everything in my code and there are no compilation errors, but when I try to run the code the console shows an error that, "Date Must not be Null". What am I doing wrong? Do I have to implement a "base" date first?

kalender = new JPanel();
kalender.setBackground(new Color(135, 206, 235));
kalender.setBounds(0, 0, 506, 250);
LayeredPane.add(kalender);
kalender.setLayout(null);
    
Termin = new Termin();
    
SimpleDateFormat sdl = new SimpleDateFormat("dd-MM-yyyy");
JDateChooser dateChooser = new JDateChooser();
dateChooser.setBounds(169, 119, 70, 20);
Termin.setDate(sdl.format(dateChooser.getDate())); // the erro must be here because with out this     
kalender.add(dateChooser);                          //line everything works
System.out.println(Termin);
    
JButton btnNext3 = new JButton("Next");
btnNext3.setBounds(215, 200, 70, 20);
kalender.add(btnNext3);
btnNext3.addActionListener(new ActionListener() {

        public void actionPerformed(ActionEvent e) {
            LayeredPane.moveToFront(kontakt);
            kalender.removeAll();
        }
        
    });

So I have a separate Class "Termin" to define all the attributes of an appointment, and I want to set the attributes date to whatever the user chooses in the Date Chooser.

I have tried to set the date in the attribute by hard coding it, but then it would not change when the user makes a selection with the date chooser.

In this line:

Termin.setDate(sdl.format(dateChooser.getDate()));

dateChooser.getDate() returns null because because no date has yet been selected. You need to detect when user has changed the date. You should use code as in this SO: Is it possible to detect a date change on a JCalendar JDateChooser field?

It should look something like:

dateChooser.getDateEditor().addPropertyChangeListener(
    new PropertyChangeListener() {
        @Override
        public void propertyChange(PropertyChangeEvent e) {
           if ("date".equals(e.getPropertyName())) {
                java.util.Date date = (java.util.Date)e.getNewValue();
                Termin.setDate(sdl.format(date));
            }
        }
    }
);