How to fill dataframe Nan values with empty list [] in pandas?

Question

This is my dataframe:

          date                          ids
0     2011-04-23  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,...
1     2011-04-24  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,...
2     2011-04-25  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,...
3     2011-04-26  Nan
4     2011-04-27  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,...
5     2011-04-28  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,...

I want to replace Nan with []. How to do that? Fillna([]) did not work. I even tried replace(np.nan, []) but it gives error:

 TypeError('Invalid "to_replace" type: \'float\'',)

Answer 1

My approach is similar to @hellpanderrr's, but instead tests for list-ness rather than using isnan:

df['ids'] = df['ids'].apply(lambda d: d if isinstance(d, list) else [])

I originally tried using pd.isnull (or pd.notnull) but, when given a list, that returns the null-ness of each element.