[jefftk]

"The system transitions from one valid state to another" is clearly false: the system only has a single state.

[mpyne]

One of the first state machine you'll ever learn about in undergrad permits transitions from a state back to itself, so I don't see this as a barrier.

[jefftk]

The claim is not "it's a state machine" but about transitioning from one valid state "to another". That requires more than one state.

[eru]

And you can implement /dev/null with multiple states, as long as you make them all behave the same way.