It's unclear why empty taglists should be handled in a special way. If the subclass or upstream did not provide any tags at all then we can still provide bitrate tags at least. Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8157>
Base classes ------------ GstBaseSink FIXME: not much point making it operate in pull mode as a generic base class I guess...