title: Python / Pyspark - Count NULL, empty and NaN
body: <p>i want to count NULL, empty and NaN values in a column.
  I tried it like this:</p>
  
  <pre><code>df.filter( (df["ID"] == "") | (df["ID"].isNull()) | ( df["ID"].isnan()) ).count()
  </code></pre>
  
  <p>But i always get this error message:</p>
  
  <pre><code>TypeError: 'Column' object is not callable
  </code></pre>
  
  <p>Does anyone have an idea what might be the problem?</p>
  
  <p>Many thanks in advance!</p>