PX4 and Dronekit no velocity Data

Hi i am trying to use dronekit with px4v1.11.0
when i am running the script to get the attitude and velocity data
i m getting Velocity: [None, None, None]. i am not able to get the numbers as i am getting for Attitude: [Roll Pitch Yaw]
may be i am missing something … someone pls help me out

Thanks