title: How do I replace a string value with a NULL in PySpark?
body: <p>I want to do something like this:</p>
  
  <pre><code>df.replace('empty-value', None, 'NAME')
  </code></pre>
  
  <p>Basically, I want to replace some value with NULL. but it does not accept None in this function. How can I do this?</p>