title: pandas query None values
body: <p>I have a dataframe with columns of different dtypes and I need to use  <code>pandas.query</code> to filter the columns.</p>
  
  <p>Columns can include missing values: <code>NaN</code>, <code>None</code> and <code>NaT</code> and I need to display the rows that contain such values. Is there a way to do this in an expression passed to <code>pandas.query</code>? I am aware that it can be done using different methods but I need to know if it is doable through the <code>query</code></p>
  
  <p>For boolean columns I was able to use a workaround by stating:</p>
  
  <pre><code>df.query('col not in (True, False)')
  </code></pre>
  
  <p>but this won't work for other types of columns. Any help is appreciated including workarounds.</p>