@connection can be NULL for this callback. Document this possibility
and describe the circumstances.
https://bugzilla.gnome.org/show_bug.cgi?id=686231
/**
* GBusNameVanishedCallback:
- * @connection: The #GDBusConnection the name is being watched on.
+ * @connection: The #GDBusConnection the name is being watched on, or
+ * %NULL.
* @name: The name being watched.
* @user_data: User data passed to g_bus_watch_name().
*
* Invoked when the name being watched is known not to have to have a owner.
*
+ * This is also invoked when the #GDBusConection on which the watch was
+ * established has been closed. In that case, @connection will be
+ * %NULL.
+ *
* Since: 2.26
*/
typedef void (*GBusNameVanishedCallback) (GDBusConnection *connection,