isn't
```
if pd.isnull(dataframe.ix['single_row', 'single_col'])  # is a value, not a Series
```
clearer? Why not just grab the single variable directly without the item call?

The issue here is funky behaviour with ix and loc could mean occasionally you weren't actually getting a length 1 Series here (say if you had dupe index/cols for whatever reason) so it'll (sometimes!) raise.