## Prework - [x] Read and abide by `drake`'s [code of conduct](https://github.com/wlandau/learndrake/blob/master/CODE_OF_CONDUCT.md). - [x] Search for duplicates among the [existing issues](https://github.com/wlandau/learndrake/issues), both open and closed. ## Description https://github.com/ropensci/drake/pull/977
