Unknown fatal error in _ParseAndCheckTwitter

[ara4n]

Traceback (most recent call last):
  File "/home/mastodon/MastodonToTwitter/env/lib/python3.4/site-packages/twitter/api.py", line 4850, in _ParseAndCheckTwitter
    data = json.loads(json_data)
  File "/usr/lib/python3.4/json/__init__.py", line 318, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.4/json/decoder.py", line 343, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.4/json/decoder.py", line 361, in raw_decode
    raise ValueError(errmsg("Expecting value", s, err.value)) from None
ValueError: Expecting value: line 1 column 1 (char 0)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "./MastodonToTwitter.py", line 371, in <module>
    new_tweets = twitter_api.GetUserTimeline(since_id = since_tweet_id, include_rts=False, exclude_replies=True)
  File "/home/mastodon/MastodonToTwitter/env/lib/python3.4/site-packages/twitter/api.py", line 765, in GetUserTimeline
    data = self._ParseAndCheckTwitter(resp.content.decode('utf-8'))
  File "/home/mastodon/MastodonToTwitter/env/lib/python3.4/site-packages/twitter/api.py", line 4860, in _ParseAndCheckTwitter
    raise TwitterError({'Unknown error: {0}'.format(json_data)})
twitter.error.TwitterError: {'Unknown error: '}