[json-glib/wip/nielsdg/add-nullable-serializable-property] serializable: Add (nullable) annotation

[Niels De Graef <nielsdg src gnome org>]

commit 725cfc3410b66bd749183b6e9e9b6a8bb0c63d0f
Author: Niels De Graef <niels degraef barco com>
Date:   Tue Jan 7 11:58:06 2020 +0100

    serializable: Add (nullable) annotation
    
    `json_serializable_serialize_property()` can return NULL, so make that
    clear in the documentation (and to GIR).

 json-glib/json-serializable.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/json-glib/json-serializable.c b/json-glib/json-serializable.c
index d7a76d6..eb7556d 100644
--- a/json-glib/json-serializable.c
+++ b/json-glib/json-serializable.c
@@ -199,8 +199,8 @@ G_DEFINE_INTERFACE (JsonSerializable, json_serializable, G_TYPE_OBJECT);
  *                                     pspec);
  * ]|
  *
- * Return value: (transfer full): a #JsonNode containing the serialized
- *   property
+ * Return value: (transfer full) (nullable): a #JsonNode containing the
+ *   serialized property, or %NULL if it should be omitted.
  *
  * Since: 0.10
  */