how can ? serialize tojson a graphic point

[azerilgar]

foreach (Graphic g in kenarbayraklayer.Graphics)
                {
                    edgeFlags = (g.Geometry as IJsonSerializable).ToJson();
                      
                }

that not works for me.
?m using sdk 3.0
is there a way serialize this geometry point like geometry.toJson(); like 3.1

thanks.