title: "TypeError: join() argument must be str or bytes, not 'NoneType'" using Magpie+Tensorflow/Python3
body: <p>I am using <a href="https://github.com/inspirehep/magpie" rel="nofollow noreferrer">magpie</a> - a multilabel classifier on Tensorflow with Word2vec. The training works fine using Python 2.7, but with Python 3.x it gives this error below. I am on Ubuntu 16.04.5 LTS, weirdly the Python 3.x code works fine on a different Ubuntu machine. I have updated my dependencies: word2vec, magpie, tf and not sure what could be going wrong. </p>
  
  <pre><code>/usr/lib/python3.5/importlib/_bootstrap.py:222: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility. Expected 96, got 88
    return f(*args, **kwds)
  Using TensorFlow backend.
  /usr/lib/python3.5/importlib/_bootstrap.py:222: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility. Expected 96, got 88
    return f(*args, **kwds)
  /usr/lib/python3.5/importlib/_bootstrap.py:222: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility. Expected 96, got 88
    return f(*args, **kwds)
  /usr/lib/python3.5/importlib/_bootstrap.py:222: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility. Expected 96, got 88
    return f(*args, **kwds)
  /usr/lib/python3.5/importlib/_bootstrap.py:222: RuntimeWarning: numpy.dtype size changed, may indicate binary incompatibility. Expected 96, got 88
    return f(*args, **kwds)
  Traceback (most recent call last):
    File "train_magpie.py", line 1, in &lt;module&gt;
      from magpie import Magpie
    File "/usr/local/lib/python3.5/dist-packages/magpie/__init__.py", line 1, in &lt;module&gt;
      from .main import Magpie
    File "/usr/local/lib/python3.5/dist-packages/magpie/main.py", line 12, in &lt;module&gt;
      from magpie.base.word2vec import train_word2vec, fit_scaler
    File "/usr/local/lib/python3.5/dist-packages/magpie/base/word2vec.py", line 7, in &lt;module&gt;
      from gensim.models import Word2Vec
    File "/usr/local/lib/python3.5/dist-packages/gensim/__init__.py", line 6, in &lt;module&gt;
      from gensim import parsing, matutils, interfaces, corpora, models, similarities, summarization
    File "/usr/local/lib/python3.5/dist-packages/gensim/parsing/__init__.py", line 7, in &lt;module&gt;
      from .preprocessing import *
    File "/usr/local/lib/python3.5/dist-packages/gensim/parsing/preprocessing.py", line 10, in &lt;module&gt;
      from gensim import utils
    File "/usr/local/lib/python3.5/dist-packages/gensim/utils.py", line 50, in &lt;module&gt;
      from smart_open import smart_open
    File "/usr/local/lib/python3.5/dist-packages/smart_open/__init__.py", line 1, in &lt;module&gt;
      from .smart_open_lib import *
    File "/usr/local/lib/python3.5/dist-packages/smart_open/smart_open_lib.py", line 45, in &lt;module&gt;
      from boto.compat import BytesIO, urlsplit, six
    File "/usr/lib/python3/dist-packages/boto/__init__.py", line 1216, in &lt;module&gt;
      boto.plugin.load_plugins(config)
    File "/usr/lib/python3/dist-packages/boto/plugin.py", line 92, in load_plugins
      for file in glob.glob(os.path.join(directory, '*.py')):
    File "/usr/lib/python3.5/posixpath.py", line 89, in join
      genericpath._check_arg_types('join', a, *p)
    File "/usr/lib/python3.5/genericpath.py", line 143, in _check_arg_types
      (funcname, s.__class__.__name__)) from None
  TypeError: join() argument must be str or bytes, not 'NoneType'
  </code></pre>