WebRTCSink custom signaller example does not panic

According to the webrtcsink-custom-signaller README , running:

cargo run --example webrtcsink-custom-signaller

should panic (the README says, "The expected output is a not-implemented panic (from imp::Signaller::start function)").

But when I run that command, it prints:

(webrtcsink-custom-signaller:110102): GLib-GObject-CRITICAL **: 22:02:23.383: Object class MyCustomWebRTCSinkSignaller doesn't implement property 'manual-sdp-munging' from interface 'GstRSWebRTCSignallableIface'

And then hangs. It seems to hang at the line:

let _msg = bus.timed_pop_filtered(gst::ClockTime::NONE, &[gst::MessageType::Eos]);

It's supposed to panic in imp.rs at:

impl SignallableImpl for Signaller {
    fn start(&self) {
        unimplemented!()
    }

But it doesn't seem to be calling this function.