[Vala] Gst.XML vapi

[vasaka gmail com]

in gstreamer.vapi

        public class XML : Gst.Object {
                            ...
                public XML ();
                [NoWrapper]
                ...
                public bool parse_file (uchar[] fname, uchar[] root);

should be

public bool parse_file (uchar[] fname, uchar[]? root);

because root can be NULL, as said in the documentation.

--
vasaka