title: To replace "None" with null in a spark dataframe in Jupyter Notebook
body: <p>I am finding difficulty in trying to replace every instance of "None" in the spark dataframe with nulls.</p>
  
  <p>My assigned task requires me to replace "None" with a Spark Null.</p>
  
  <p>And when I tried using:</p>
  
  <p><code>data_sdf = data_sdf.na.fill("None", Seq("blank"))</code></p>
  
  <p>it failed. Any suggestions on how should I handle this issue?</p>
  
  <p>This is my sample spark dataframe I am required to work on-</p>
  
  <pre><code>+--------------------+---------+---------+---------+---------+---------+---------+---------+
  |         business_id|   monday|  tuesday|wednesday| thursday|   friday| saturday|   sunday|
  +--------------------+---------+---------+---------+---------+---------+---------+---------+
  |FYWN1wneV18bWNgQj...|7:30-17:0|7:30-17:0|7:30-17:0|7:30-17:0|7:30-17:0|     None|     None|
  |He-G7vWjzVUysIKrf...| 9:0-20:0| 9:0-20:0| 9:0-20:0| 9:0-20:0| 9:0-16:0| 8:0-16:0|     None|
  |KQPW8lFf1y5BT2Mxi...|     None|     None|     None|     None|     None|     None|     None|
  </code></pre>