🚀 go-pugleaf

I need to open a modal Dialog inside a DesktopPane. I am tried to use
createInternalFrame() or showInternal ... but I get an exception. A code
example follows, and the exception is at the end. The problem is in the
' this.getContentPane() ' argument. I don't know what I should put
there. The parent of this dialog is a JInternalFrame.

 JOptionPane pane = new JOptionPane("This is a test");
 JInternalFrame dialog = pane.createInternalFrame(this.getContentPane(),
"title here");
 dialog.show();


Exception occurred during event dispatching:
java.lang.IllegalArgumentException: cannot add to layout: constraint
must be a string (or null)
 at java.awt.BorderLayout.addLayoutComponent(BorderLayout.java:205)
 at java.awt.Container.addImpl(Container.java:319)
 at com.sun.java.swing.JLayeredPane.addImpl(JLayeredPane.java:153)
 at java.awt.Container.add(Container.java:219)
 at
com.sun.java.swing.JOptionPane.createInternalFrame(JOptionPane.java:1055)

 at
ittc.phoenix.phclient.dataedit.AgreementEdit.disclosureButton_actionPerformed(AgreementEdit.java:583)

 at
ittc.phoenix.phclient.dataedit.AgreementEdit$4.actionPerformed(AgreementEdit.java:253)

 at
com.sun.java.swing.AbstractButton.fireActionPerformed(AbstractButton.java:860)

 at
com.sun.java.swing.AbstractButton$ForwardActionEvents.actionPerformed(AbstractButton.java:895)

 at
com.sun.java.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:338)

 at
com.sun.java.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:230)

 at
com.sun.java.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:156)

 at java.awt.Component.processMouseEvent(Component.java:2404)
 at java.awt.Component.processEvent(Component.java:2249)
 at java.awt.Container.processEvent(Container.java:878)
 at java.awt.Component.dispatchEventImpl(Component.java:1781)
 at java.awt.Container.dispatchEventImpl(Container.java:923)
 at java.awt.Component.dispatchEvent(Component.java:1708)
 at
java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:1559)
 at
java.awt.LightweightDispatcher.processMouseEvent(Container.java:1463)
 at java.awt.LightweightDispatcher.dispatchEvent(Container.java:1395)
 at java.awt.Container.dispatchEventImpl(Container.java:910)
 at java.awt.Window.dispatchEventImpl(Window.java:492)
 at java.awt.Component.dispatchEvent(Component.java:1708)
 at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)