* @flags: Flags describing how to subscribe to the signal (currently unused).
* @callback: Callback to invoke when there is a signal matching the requested data.
* @user_data: User data to pass to @callback.
- * @user_data_free_func: Function to free @user_data with when subscription is removed or %NULL.
+ * @user_data_free_func: (allow-none): Function to free @user_data with when
+ * subscription is removed or %NULL.
*
* Subscribes to signals on @connection and invokes @callback with a
* whenever the signal is received. Note that @callback
* @object_path: The object path to register at.
* @interface_info: Introspection data for the interface.
* @vtable: (allow-none): A #GDBusInterfaceVTable to call into or %NULL.
- * @user_data: Data to pass to functions in @vtable.
+ * @user_data: (allow-none): Data to pass to functions in @vtable.
* @user_data_free_func: Function to call when the object path is unregistered.
* @error: Return location for error or %NULL.
*