title: python Flask, TypeError: 'NoneType' object is not subscriptable
body: <p>I'm studying Flask very recently and trying to create API.<br>
  However, when It request json data, this error occurs.<br>
      <strong>if content['words'] is not None:<br>
  TypeError: 'NoneType' object is not subscriptable</strong>
  <br>
  could anyone can help this?<br>
  Thanks<br>
  my code is below:</p>
  
  <pre class="lang-py prettyprint-override"><code>
      @app.route("/process",methods=['GET', 'POST'])
  def process():
      content = request.json
      words = {}
      if content['words'] is not None:
          for data in content['words'].values():
              words[data['word']] = data['weight']
      process_from_text(content['text'], content['maxCount'], content['minLength'], words)
      result = {'result':True}
      return jsonify(result
  
  </code></pre>