I try to get the popup menu from the main menubar in the following BASIC macro,
but throw a Basic runtime error.

Step to reproduce:
1. File a new document and run the following BASIC macro:

Sub Main
	dim oMenuBar
	dim nItemid
	dim oPopMenu
	oMenuBar =
thiscomponent.getcurrentcontroller.getframe.layoutmanager.getelement("private:resource/menubar/menubar").XMenuBar
	nItemid = oMenuBar.getItemId(0)
	oPopMenu = oMenuBar.getPopupMenu(nItemid)
	msgbox oPopMenu.isPopupMenu
End Sub

2. It throws a "Basic runtime error" in the macro line:
msgbox oPopMenu.isPopupMenu