title: Unable to find the word that I added to the Huggingface Bert tokenizer vocabulary
body: <p>I tried to add new words to the <code>Bert tokenizer vocab</code>. I see that the length of the vocab is increasing, however I can't find the newly added word in the vocab.</p>
  <pre><code>tokenizer.add_tokens(['covid', 'wuhan'])
  
  v = tokenizer.get_vocab()
  
  print(len(v))
  'covid' in tokenizer.vocab
  </code></pre>
  <p>Output:</p>
  <pre><code>30524
  
  False
  </code></pre>