How to get RTPSession from rtpbin

[kingle-zhuang]

public class RTPSession extends GstObject
{
    protected RTPSession(Initializer init) {
        super(init);
    }

    protected RTPSession(Handle handle, boolean needRef) {
        super(handle, needRef);
    }
}

        RTPSession session = this.rtpbin.emit(RTPSession.class, "get-internal-session", 1);
        session.connect(name, RTCP_LISTENER.class, listener, new GstAPI.GstCallback() {
            @SuppressWarnings("unused")
            public void callback(Element element, Buffer buffer, boolean early, GPointer data) {
                listener.handle(element, buffer, early, data);
            }
        });

        for session still return null

        how to register class & how to get  RTPSession instance