make_transition on unsaved fails

[ramn]

Problem:

If I have log_transitions = True in my state machine, and then make_transition on an unsaved model object, we crash since 'self' (model object) doesn't have an id but an id is assumed here:
model_methods.py, method make_transition, line 151:
_state_log_model.objects.create(
on=self,

Discussion:
Perhaps we could have an explicit exception for this case, stating that the object needs an id/to be saved beforehand.

[jonathanslenders]

Thanks for the bug report! Indeed, we assumed that an object needs to be saved before running any state transitions on it. I will throw an exception instead.