Where is LiveChildOrSelf

I want to use LiveChildOrSelf from the interface ICinemachineCamera like seen here: https://docs.unity3d.com/Packages/com.unity.cinemachine@2.1/api/Cinemachine.ICinemachineCamera.html

How ever when I go for the following line : Camera.main.GetComponent<Cinemachine.CinemachineBrain>().ActiveVirtualCamera.IsLiveChild is not found. I'm on cinemachine 2.2.8 and unity 2018.3.4f1

 

I cant. It seems the property LiveChildOrSelf does not exist in ICinemachineCamera.