Make request optional in transition_to_state()

[zupo]

The transition_to_state() method is more or less just a permissions wrapper around the _transition_to_state() method that does the bulk of the work.

The _transition_to_state() has the request parameter optional, while the transition_to_state() does not. I'd like to make the request parameter optional also in transition_to_state() so that I don't have to pass None in application code that does not use the permissions checker.

There are two approaches I see:

1. Changing the method signature:

-def transition_to_state(self, content, request, to_state, context=None, guards=(), skip_same=True):
+def transition_to_state(self, content, to_state, request=None, context=None, guards=(), skip_same=True):

But this is backwards incompatible and is likely gonna break application code that relies on positioning of to_state and request parameters in transition_to_state() method.

1. Making to_state optional too, and failing if it is None:

-def transition_to_state(self, content, request, to_state, context=None, guards=(), skip_same=True):
+def transition_to_state(self, content, request=None, to_state=None, context=None, guards=(), skip_same=True):
+    if not to_state:
+        raise KeyError('"to_state" is a required parameter')

Which approach is better? Suggestions for tackling this issue some other way?