If you happen to have a "payloader" element named "payX" that is not a proper GstRTPBasePayloader then you will not have a "pt" property.
This means you might get a scary output on your console:
GLib-GObject-CRITICAL **: 13:56:00.598: g_object_get_is_valid_property: object class 'GstQueue' has no property named 'pt'
This is however acceptable behavior, so I think a
GST_WARNING (same as
for when we cannot find "stats" property on the payloader in
gst_rtsp_stream_get_rtpinfo) would do fine.