`undefined` when using RFC4180 in Mix Task

[kevinkirkup]

When generating PLTs

Compiling 44 files (.ex)
     warning: NimbleCSV.RFC4180.dump_to_iodata/1 is undefined (module NimbleCSV.RFC4180 is not available or is yet to be defined)
     │

Not doing anything fancy here.

    [headers | rows]
    |> CSVParser.dump_to_iodata()
    |> IO.iodata_to_binary()
    |> then(&File.write("output.csv", &1))

Any help would be appreciated.