plug Plug.Static,
    at: "/",
    from: Application.get_env(:myapp, :static_files),
    gzip: true,
    only: ~w(css fonts images js favicon_16x16.png robots.txt)

** (exit) an exception was raised:
    ** (ArgumentError) unknown application: nil
        (elixir 1.10.3) lib/application.ex:885: Application.app_dir/1
        (plug 1.10.0) lib/plug/static.ex:393: Plug.Static.path/2
        (plug 1.10.0) lib/plug/static.ex:176: Plug.Static.call/2
        (creo 1.0.0) lib/creo_web/endpoint.ex:1: CreoWeb.Endpoint.plug_builder_call/2
        (creo 1.0.0) lib/plug/debugger.ex:132: CreoWeb.Endpoint."call (overridable 3)"/2
        (creo 1.0.0) lib/creo_web/endpoint.ex:1: CreoWeb.Endpoint.call/2
        (phoenix 1.5.1) lib/phoenix/endpoint/cowboy2_handler.ex:64: Phoenix.Endpoint.Cowboy2Handler.init/4
        (cowboy 2.7.0) /home/mike/code/cg/web/creo/backend/deps/cowboy/src/cowboy_handler.erl:41: :cowboy_handler.execute/2

@static_path Application.get_env(:my_app, :my_key)

plug Plug.Static,
  ...