[vala/0.34] gio-2.0: Cherry-pick some DBusProxy fixes from 0.40

[Rico Tzschichholz <ricotz src gnome org>]

commit 100b7b0ffe7c6aec4948063a2aaf3ae0d32f399e
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Wed Feb 14 11:26:35 2018 +0100

    gio-2.0: Cherry-pick some DBusProxy fixes from 0.40

 vapi/gio-2.0.vapi |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/vapi/gio-2.0.vapi b/vapi/gio-2.0.vapi
index 9963695..0ac9d3f 100644
--- a/vapi/gio-2.0.vapi
+++ b/vapi/gio-2.0.vapi
@@ -974,16 +974,16 @@ namespace GLib {
                public static async GLib.DBusProxy create_for_bus (GLib.BusType bus_type, GLib.DBusProxyFlags 
flags, GLib.DBusInterfaceInfo? info, string name, string object_path, string interface_name, 
GLib.Cancellable? cancellable = null) throws GLib.IOError;
                [CCode (has_construct_function = false)]
                public DBusProxy.for_bus_sync (GLib.BusType bus_type, GLib.DBusProxyFlags flags, 
GLib.DBusInterfaceInfo? info, string name, string object_path, string interface_name, GLib.Cancellable? 
cancellable = null) throws GLib.Error;
-               public GLib.Variant get_cached_property (string property_name);
+               public GLib.Variant? get_cached_property (string property_name);
                [CCode (array_length = false, array_null_terminated = true)]
-               public string[] get_cached_property_names ();
+               public string[]? get_cached_property_names ();
                public unowned GLib.DBusConnection get_connection ();
                public int get_default_timeout ();
                public GLib.DBusProxyFlags get_flags ();
-               public GLib.DBusInterfaceInfo get_interface_info ();
+               public unowned GLib.DBusInterfaceInfo? get_interface_info ();
                public unowned string get_interface_name ();
                public unowned string get_name ();
-               public string get_name_owner ();
+               public string? get_name_owner ();
                public unowned string get_object_path ();
                [CCode (cname = "g_dbus_proxy_new", finish_function = "g_dbus_proxy_new_finish")]
                public static async GLib.DBusProxy @new (GLib.DBusConnection connection, GLib.DBusProxyFlags 
flags, GLib.DBusInterfaceInfo? info, string? name, string object_path, string interface_name, 
GLib.Cancellable? cancellable = null) throws GLib.IOError;