I noticed that Adobe's panels go blank when there's no document open. I'd like to do the same. Perhaps this should be a feature request for the panel class, but in the meantime I would guess a function to simply switch the visibility of the panel's widgets true or false is the best approach. Is there a simpler way I've overlooked? Thanks...
There is no automated way to achieve this and we won't be adding one, but you can do it manually by subscribing to the right document notifiers and hide/show the widgets when appropriate.
We have the WidgetGroup class to make it more convenient to apply the same modifications to a number of widgets all at once, but visibility is not currently supported by that class. I'll add it to the TODO list.