defaultdict(None)

defaultdict requires a callable as argument that provides the default-value when invoked without arguments. None is not callable. What you want is this:

defaultdict(lambda: None)

In this use case, don't use defaultdict at all -- a plain dict will do just fine:

states = {}
if new_state_1 != states.get("State 1"):
    dispatch_transition()

The dict.get() method returns the value for a given key, or a default value if the key is not found. The default value defaults to None.