The if/else check deleted in this commit was used in an earlier
version of the view to let the user filter by whether data was missing
on a given facet. In other words, we wanted to be able
to send [something]__isnull=True in the query.
This was superceded with another appraoch, where some option representing
missing data was added to choices in a select field, and translated
into the query by means of an annotation.