A few notes on why this is so: - Keywords (i.e. `:vehicles`) can be used as getter functions, as covered in the OP. - mapcat (like most collection functions i

A few notes on why this is so: - Keywords (i.e. `:vehicles`) can be used as getter functions, as covered in the OP. - mapcat (like most collection functions in clojure) treats `nil` as an empty sequence