@Override
	public Dimension getPreferredSize() {
		if (viewport == null) {
			viewport = getViewport();
			if (viewport != null) {
				viewport.addChangeListener(this);
			}
		}
		return model.getPreferredViewSize();
	}
Returns the last visible layout or null if there are no visible layouts

@return the last visible layout
Ghidra/Framework/Docking/src/main/java/docking/widgets/fieldpanel/FieldPanel.java