[glib] gsettingsschema: Add a missing (nullable) annotation

[Philip Withnall <pwithnall src gnome org>]

commit e34884e364f572d7d891f584a479e583114190aa
Author: Philip Withnall <withnall endlessm com>
Date:   Wed Oct 11 13:09:53 2017 +0100

    gsettingsschema: Add a missing (nullable) annotation
    
    Spotted as part of https://bugzilla.gnome.org/show_bug.cgi?id=725014.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>

 gio/gsettingsschema.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gio/gsettingsschema.c b/gio/gsettingsschema.c
index d57c08d..5fbc2ed 100644
--- a/gio/gsettingsschema.c
+++ b/gio/gsettingsschema.c
@@ -376,7 +376,7 @@ initialise_schema_sources (void)
  * lookups performed against the default source should probably be done
  * recursively.
  *
- * Returns: (transfer none): the default schema source
+ * Returns: (transfer none) (nullable): the default schema source
  *
  * Since: 2.32
  **/