Cannot use gdbus command against same arguments of dbus-send

[Germano Massullo]

I have been told that dbus-send use session bus and I was using gdbus
against system bus, so I solved with

$ gdbus call --session --dest org.gnome.Mutter.IdleMonitor
--object-path /org/gnome/Mutter/IdleMonitor/Core --method
org.gnome.Mutter.IdleMonitor.GetIdletime