title: How to create dataframe in pandas that contains Null values
body: <p>I try to create below dataframe that deliberately lacks some piece of information. That is, <code>type</code> shall be empty for one record.</p>
  
  <pre><code>df = {'id': [1, 2, 3, 4, 5],
        'created_at': ['2020-02-01', '2020-02-02', '2020-02-02', '2020-02-02', '2020-02-03'],
        'type': ['red', NaN, 'blue', 'blue', 'yellow']}
  
  df = pd.DataFrame (df, columns = ['id', 'created_at','type', 'converted_tf'])
  </code></pre>
  
  <p>Works perfectly fine when I put all the values but I keep getting errors with <code>NaN</code>, <code>Null</code>, <code>Na</code>, <code></code> etc.</p>
  
  <p>Any idea what I have to put?</p>