title: An error about TypeError: expected str, bytes or os.PathLike object, not NoneType
body: <p>I tried to correct English grammar by running a model.</p>
  
  <p>My development environment is <code>Linux</code> + <code>Anaconda3</code> + <code>Python 3.6</code> + <code>CUDA 9.0</code> + <code>tensorflow1.9.0</code></p>
  
  <p>After I ran the model, there was the following problem with the test:</p>
  
  <pre><code>Traceback (most recent call last):
    File "./generate.py", line 236, in &lt;module&gt;
      main(args)
    File "./generate.py", line 93, in main
      fluency_scorer = FluencyScorer(args.lang_model_path, args.lang_model_data)
    File "/home/gpower/zhangtianjiu/NLP/pytorch-human-performance-gec-master/fairseq-scripts/fluency_scorer.py", line 58, in __init__
      self.task = tasks.setup_task(self.args)
    File "/home/gpower/zhangtianjiu/NLP/pytorch-human-performance-gec-master/fairseq/fairseq/tasks/__init__.py", line 19, in setup_task
      return TASK_REGISTRY[args.task].setup_task(args)
    File "/home/gpower/zhangtianjiu/NLP/pytorch-human-performance-gec-master/fairseq/fairseq/tasks/language_modeling.py", line 90, in setup_task
      dictionary = Dictionary.load(os.path.join(args.data, 'dict.txt'))
    File "/home/gpower/anaconda3/envs/tf/lib/python3.6/posixpath.py", line 78, in join
      a = os.fspath(a)
  TypeError: expected str, bytes or os.PathLike object, not NoneType
  </code></pre>
  
  <p>How should I solve this problem? </p>