Some GstAppSink functions have incorrect return nullability in Vala

In Vala, GstAppSink.pull_sample() and some other fucntions specify non-nullable Gst.Sample in the docs and bindings when in reality, the return is nullable and should be Gst.Sample?. I'm not very familiar with GObject annotations but perhaps the problem lies there?

Valac version is Vala 0.40.23 Meson version is 0.57.2 GStreamer version is 1.14.5 Platform is aarch64 Ubuntu 18.04 (Linux for Tegra)