It can be NULL. ::create-menu-proxy gave an example of when a NULL proxy
menu item could be useful, but the accessors did not annotate it as such.
* @menu_item_ids must match ensures that a #GtkToolItem
* will not inadvertently change a menu item that they did not create.
*
- * Returns: (transfer none): The #GtkMenuItem passed to
+ * Returns: (transfer none) (nullable): The #GtkMenuItem passed to
* gtk_tool_item_set_proxy_menu_item(), if the @menu_item_ids
* match.
*
/**
* gtk_tool_item_set_proxy_menu_item:
- * @tool_item: a #GtkToolItem
+ * @tool_item: (nullable): a #GtkToolItem
* @menu_item_id: a string used to identify @menu_item
* @menu_item: a #GtkMenuItem to be used in the overflow menu
*