InternalFrame em branco

package com.gui;

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;

import net.miginfocom.swing.MigLayout;

public class GUI extends JFrame {

	JDesktopPane desk;
	JPanel panel;
	
	public static void main(String[] args) {
		
		EventQueue.invokeLater(new Runnable(){

			@Override
			public void run() {
				
				new GUI().setVisible(true);
				
			}
					
		});
		
	}
	
	public GUI(){
			
		this.initFrame();
	
		this.pack();
		
		this.setExtendedState(MAXIMIZED_BOTH);
		
	}
	
	public void initFrame(){
			
		this.desk = this.getDesktopPane();
		
		this.panel = this.getPanel();
					
		this.setContentPane(this.panel);
		
		JMenuBar menuBar = new JMenuBar();
		this.setJMenuBar(menuBar);
		
		JMenu menu = new JMenu("Teste");
		menuBar.add(menu);
		
		JMenuItem menuItem = new JMenuItem("Internal");
		menuItem.addActionListener(new ActionListener(){

			@Override
			public void actionPerformed(ActionEvent e) {
				// TODO Auto-generated method stub
				
				GUI.this.panel.add(GUI.this.desk, "dock center");
			}
			
		});
		
		menu.add(menuItem);
		
	}
	
	public JPanel getPanel(){
		
		JPanel panel = new JPanel();
		
		MigLayout mig = new MigLayout("","[grow]", "[grow]");
		
		panel.setLayout(mig);
		
		return panel;
		
	}
	
	public JDesktopPane getDesktopPane(){
			
		Internal internalFrame = new Internal();
        				
        this.desk = new JDesktopPane();
      
        this.desk.add(internalFrame);
        
        internalFrame.setVisible(true);
		
		return desk;		
	}
	
}

package com.gui;

import javax.swing.JInternalFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

import net.miginfocom.swing.MigLayout;

public class Internal extends JInternalFrame {

	Internal(){
		
		this.setVisible(true);
		
		//this.setMaximizable(this.maximizable);
		
		this.initInternal();
		
		this.setResizable(false);
		
	}
	
	public void initInternal(){
		
		JLabel label = this.getLabel();
		label.setName("Nome: ");
		
		JTextField text = this.getTextField();
		
		
		JPanel panel = this.getPanel();
		panel.add(label);
		panel.add(text);
		
		this.setContentPane(panel);
				
		
	}
	
	public JLabel getLabel(){
		
		JLabel label = new JLabel();
		
		return label;
		
	}
	
	public JPanel getPanel(){
		
		JPanel panel = new JPanel();
		
		panel.setLayout(new MigLayout("", "[grow]", "[grow]"));
		
		return panel;
	}
	
	public JTextField getTextField(){
		
		JTextField textField = new JTextField();
		
		return textField;
		
	}
}