title: Replacing None with a list within a dataframe
body: <p>I have the below dataframe which comes from a JSON</p>
  <hr />
  <pre><code>0        [0, 5.9, 4]       [1, 6, 23]      [2, 6.2, 2]
  1      [0, 48, 3.11]      [1, 50, 10]    [2, 55, 13.1]
  2   [0, 1.42, 90.26]  [1, 1.43, 91.8]   [2, 1.44, 121]
  3    [0, 970, 18.41]   [1, 990, 1.53]             None
  4    [0, 970, 18.42]   [1, 990, 1.55]  [2, 1000, 22.5]
  5     [0, 740, 9.37]   [1, 990, 1.53]             None
  6     [0, 740, 9.37]   [1, 900, 2.21]   [2, 990, 1.55]
  7    [0, 970, 18.45]    [1, 990, 1.6]             None
  8     [0, 740, 9.39]   [1, 990, 2.55]             None
  9     [0, 970, 18.4]    [1, 990, 1.6]             None
  10      [0, 42, 1.1]    [1, 85, 1.91]    [2, 90, 1.04]
  </code></pre>
  <hr />
  <p>trying to format ready for db insertion, i am splitting using .tolist() but getting error for None entries.</p>
  <p>tried fillna and replace to insert a dummy list i.e. [0,0,0] but will only let me replace with a string. Any suggestions welcome.</p>
  <p>this works</p>
  <p>#df_split_batl = df_split_batl.fillna('xx')
  #df_split_batl = df_split_batl.replace('xx','yy')</p>
  <p>but these dont</p>
  <p>#df_split_batl = df_split_batl.fillna([0,0,0])</p>
  <p>#df_split_batl = df_split_batl.fillna('xx')</p>
  <p>#df_split_batl = df_split_batl.replace('xx',[0,0,0])</p>