Não consegui abrir essa classe

Tenho um Class JanelaPrincipal com um menu, que quando clico em Cadastrar deveria chamar a classe JanelaCadastro, mas não funciona,  não  sei pq, aparece o seguinte erro:

[color=“red”]Exception in thread “AWT-EventQueue-0” java.lang.NullPointerException

at java.awt.Container.addImpl(Unknown Source)

at java.awt[/color].Container.add(Unknown Source)

at JanelaCadastro.<init>(JanelaCadastro.java:36)

at Janelas.getJanelaCadastro(Janelas.java:25)

at JanelaPrincipal.Cadastrar(JanelaPrincipal.java:105)

at JanelaPrincipal.actionPerformed(JanelaPrincipal.java:94)

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.AbstractButton.doClick(Unknown Source)

at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)

at javax.swing.plaf.basic.BasicMenuItemUI$Handler.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.dispatchEvent(Unknown Source)

at java.awt.EventDispatchThread.pumpOneEventForHierarchy(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)[/color]

import javax.swing.JFrame;

import java.awt.Container;

import java.awt.FlowLayout;

import javax.swing.JButton;

import javax.swing.JLabel;

import javax.swing.JTextArea;

import javax.swing.JTextField;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

public class JanelaCadastro extends JFrame implements ActionListener{

JButton Cadastrar;

JButton Cancelar;

JLabel Lmarca;

JTextField Marca;

JLabel Lmodelo;

JTextField Modelo;

JLabel Lcor;

JTextField Cor;

JLabel Lano;

JTextField Ano;

JLabel Lobservacoes;

JTextArea Observacoes;

Cadastrar = new JButton("Cadastrar");
Cancelar = new JButton("Cancelar");
Cadastrar.addActionListener(this);
Cancelar.addActionListener(this);
Container c = getContentPane();
c.setLayout(new FlowLayout());
c.add(Lmarca);
c.add(Marca);
c.add(Lmodelo);
c.add(Modelo);
c.add(Lcor);
c.add(Cor);
c.add(Lano);
c.add(Ano);
c.add(Lobservacoes);
c.add(Observacoes);
c.add(Cadastrar);
c.add(Cancelar);
pack();

}