DrakPanel throws an error when reopened with the same shell

[GoogleCodeExporter]

What steps will reproduce the problem?
1.create a shell
2.create a DarkPanel or a BlurredPanel
3.show the panel then hide it
4.create a new DarkPanel and show it 

What is the expected output? What do you see instead?
it should be able to show the DarkPanel 

What version of the product are you using? On what operating system?
latest

Please provide any additional information below.
when looked into the code I have found that a key DARK_PANEL_KEY is set to the 
shell but this key is never put at null when hiding the panel.
I think this is a slite modification something  like 
this.parent.setData(DARK_PANEL_KEY, null); in the hide method.
Thank you 

Original issue reported on code.google.com by rhadjamor@gmail.com on 3 Mar 2015 at 3:26

[lcaron]

This is not the correct way to use it:

• Create a shell
• Create a darkpanel or a blurpanel attached to this shell
• When you need it, call show() or hide()

you don't need to recreate the panels