<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_menu_item(self):
 """ Utilised by Wagtail's 'register_menu_item' hook to create a menu for this group with a SubMenu linking to listing pages for any associated ModelAdmin instances """

        if self.modeladmin_instances:
            submenu = SubMenu(self.get_submenu_items())
            return GroupMenuItem(self, self.get_menu_order(), submenu)