mutter/gnome-shell fail to start, can't find 'emulate-middle' in 'org.gnome.desktop.peripherals.mouse'
Both gnome-shell and mutter fail to start if using the mutter master branch:
(gnome-shell:11132): GLib-GIO-ERROR **: 14:52:57.209: Settings schema 'org.gnome.desktop.peripherals.mouse' does not contain a key named 'emulate-middle'