Hi,
while it's ok if you don't abuse it, it's still far from ideal.
instead, you should send a global event "PLAYER / DIED" from the fsm that knows about the death of the player, somewhere there is an fsm that is responsible for handling the logic of the death, this fsm should then be responsible to fire that global event for any other interested fsm to know about this.
then other fsm simply have that global event as a global transition on a state and will be informed properly without messing with checking for null on a gameobject.
Bye,
Jean