why I can't pass the param AnimationEvent.objectReferenceParameter,it's always null in even

code is simple just like this:

var evt = new AnimationEvent();
evt.time = eventTime;
evt.functionName = eventName;
evt.objectReferenceParameter = data;
clip.AddEvent(evt);

data is base on UnityEngine.Object.I log objectReferenceParameter in event,it`s aways null.any one know the reason?

Subclass data from ScriptableObject instead of UnityEngine.Object and it should work.