title: Filling null values in multiple dataframe columns based on condition
body: <p>So I wrote a function that fills any null values in 2 dataframe columns baded on a condition being met. I've written unit tests, they all work.</p>
  
  <p>When running it on actual data, it sometimes leads to a <code>ValueError: cannot set using a list-like indexer with a different length than the value</code></p>
  
  <p>I'm confused because my unit tests pass. The code is essentially this:
  <code>df.loc[df['column'].isin(column_values_to_update), ['col2', 'col3']] = df[['col2', 'col3']].fillna(0)</code></p>
  
  <p>It works when <code>column_values_to_update</code> is empty, it works when its full...yet when running on certain datasets, I get the ValueError and I'm not sure why....I've reset the index before getting to this point and no luck.</p>
  
  <p>Anyone have any idea why sometimes this error can arise, and sometimes it doesn't? Let me know if you need more info...</p>