* @cancellable: optional #GCancellable object, %NULL to ignore.
* @error: a #GError location to store the error occurring, or %NULL to
* ignore.
- * @first_property_name: the name of the first property, or %NULL if no
+ * @first_property_name: (allow-none): the name of the first property, or %NULL if no
* properties
* @...: the value if the first property, followed by and other property
* value pairs, and ended by %NULL.