Problem with WindowBuilder

I'm using Eclipse Kepler + Window Builder to edit a JFrame, leaving the "Source" tab and go to "Design" I'm getting the following error.

An exception happened during evaluation of constructor JFrame() using arguments {}. 
    java.lang.NullPointerException
        at java.beans.MethodRef.get(Unknown Source)
        at java.beans.PropertyDescriptor.getWriteMethod(Unknown Source)

Class Code (automatically generated by Eclipse after project creation)

    package br.com.nome_pc;

    import java.awt.BorderLayout;
    import java.awt.EventQueue;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    import javax.swing.border.EmptyBorder;

    public class Main extends JFrame {
    private JPanel contentPane;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Main frame = new Main();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */
    public Main() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        contentPane.setLayout(new BorderLayout(0, 0));
        setContentPane(contentPane);
    }

}