pandas series,isnull() is not working inside list comprehension : <p>for the following simple code:</p>

<pre><code>drop_cols = [col for col in train.columns if col[0] == 'V' and train[col].isnulll().sum()/len(train) &gt; 0.76]
drop_cols
</code></pre>

<p>I get this error:</p>

<blockquote>
  <p>AttributeError                            Traceback (most recent call
  last)  in ()
  ----> 1 drop_cols = [col for col in train.columns if col[0] == 'V' and train[col].isnulll().sum()/len(train) > 0.76]
        2 drop_cols</p>
  
  <p> in (.0)
  ----> 1 drop_cols = [col for col in train.columns if col[0] == 'V' and train[col].isnulll().sum()/len(train) > 0.76]
        2 drop_cols</p>
  
  <p>C:\Anaconda3\lib\site-packages\pandas\core\generic.py in
  <strong>getattr</strong>(self, name)    5065             if self._info_axis._can_hold_identifiers_and_holds_name(name):    5066<br>
  return self[name]
  -> 5067             return object.<strong>getattribute</strong>(self, name)    5068     5069     def <strong>setattr</strong>(self, name, value):</p>
  
  <p>AttributeError: 'Series' object has no attribute 'isnulll'</p>
</blockquote>

<p>isnull() is working elsewhere. What is the cause and fix for this?</p>
