'Override UnitHelper\'s create_session_mock method.
We want all methods to return an instance of the NullObject. This
class has a dummy ``__iter__`` implementation which we want for
methods that iterate over the results of a response.'

def create_session_mock(self, *args):

    session = super(UnitIteratorHelper, self).create_mocked_session(*args)
    null = NullObject()
    session.delete.return_value = null
    session.get.return_value = null
    session.patch.return_value = null
    session.post.return_value = null
    session.put.return_value = null
    return session
