'Session as Lazy property: check that django.contrib.sessions is installed'

@property
def session(self):

    if (not apps.is_installed('django.contrib.sessions')):
        raise EnvironmentError('Add    django.contrib.sessions    to    the    INSTALLED_APPS    to    use    session')
    if (not self._session):
        self._session = session_for_reply_channel(self.reply_channel)
    return self._session
