Cannot get answer revisions

[graipher]

While trying to take a look at an answers revisions, I encountered this:

import stackexchange
se = stackexchange.Site("CodeReview", API_KEY)
user = se.user(USER_ID)
a = user.answers.fetch()[0]
a.revisions.fetch()

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "build/bdist.linux-x86_64/egg/stackexchange/models.py", line 41, in __repr__

AttributeError: 'PostRevision' object has no attribute 'is_question'