title: to_list not working with pandas when null values in pandas
body: <pre><code>df = pd.DataFrame({'a':[None,1, 2], 'b':[None, (1,2), (3,4)]}) 
  
  
      a   b
  0   NaN None
  1   1.0 (1, 2)
  2   2.0 (3, 4)
  </code></pre>
  <p>I want to set the tuple in the column be to each have their own column. However, I have an issue with my approach</p>
  <pre><code>df[['b1', 'b2']] = pd.DataFrame(df['b'].tolist(), index=df.index)
  
  ValueError: Columns must be same length as key
  </code></pre>
  <p>I tried to fillna will an empty tuple, but it won't take a tuple. How can I make this work?</p>