title: How to drop rows with nulls in one column pyspark
body: <p>I have a dataframe and I would like to drop all rows with NULL value in one of the columns (string). I can easily get the count of that:</p>
  
  <pre><code>df.filter(df.col_X.isNull()).count()
  </code></pre>
  
  <p>I have tried dropping it using following command. It executes but the count still returns as positive</p>
  
  <pre><code>df.filter(df.col_X.isNull()).drop()
  </code></pre>
  
  <p>I tried different attempts but it returns 'object is not callable' error. </p>