Error or null geometry when lng,lat not detected?

In previous versions, this module threw an error when lng,lat were not detected. The documentation suggests this still should happen:

Err is non-falsy if latitude and longitude values cannot be detected or if there are invalid rows in the file.

However, I think commit https://github.com/mapbox/csv2geojson/commit/ee8d854540c5733bbc79c1f7678228988b850dc5 changed this behavior. The module now returns a null geometry. However, that commit did not update the documentation, and it left the relevant test in a strange place, where its description no longer matches its outcome.

So @tmcw I'm wondering which route you think would be best for this module. Should we document and clearly test the actual current behavior — not erroring, instead returning null geometry — or go back to the way things were — erroring?

Compare the current behavior with the documentation and inspect the relevant test identified in commit ee8d854540c5733bbc79c1f7678228988b850dc5. First determine whether missing lng,lat values should produce an error or null geometry. Done means the chosen behavior, documentation, and test description agree.