Can't clean JLabel

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I need to clean my labelResult each time on textField Action, but on the first time it adds 'null' in front of string and then - prints new string right after. Please help.

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
 
public class Frame extends JFrame implements ActionListener {
boolean isDirect = true;
String[] typeStr = {"direct", "invert"};
JLabel labelTip = new JLabel("Choose 'direct' OR 'invert' to print your next line in   direct order or inverted respectively.");
JTextField textField = new JTextField("Some text!", 40);
JComboBox comboBox = new JComboBox(typeStr);
EventProcessing eventProcessing = new EventProcessing();
JLabel labelResult = new JLabel();
 
public Frame() {
    setLayout(new BorderLayout());
    getContentPane().add(labelTip, BorderLayout.PAGE_START);
    getContentPane().add(comboBox, BorderLayout.CENTER);
    getContentPane().add(textField, BorderLayout.AFTER_LINE_ENDS);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    textField.addActionListener(this);
 
    pack();
}
 
public void actionPerformed(ActionEvent e) {
    getContentPane().remove(labelResult);
    labelResult = new JLabel();
    labelResult.setText("");
    if (!(comboBox.getSelectedItem()).equals("direct")) {
        isDirect = false;
    } else {
        isDirect = true;
    }
    labelResult.setText(eventProcessing.action(isDirect, textField.getText()));
    getContentPane().add(labelResult, BorderLayout.PAGE_END);
 
    pack();
 
}
 
}