All channels values are 'None'

Hi, guys.
I’ve set up SITL on Windows and connected it with FlightGear, as it’s described here. Now I can connect to SITL using dronekit from another computer in the same network, but all the channels values are ‘None’, and even when I use channel overriding. In that case the plane turns left/right using the overridden values, but when I print those values, they are ‘None’.
I would like to know if it’s OK or I am doing something wrong.