Changeset doesn't track changes. Changes are nil. about arc_ecto HOT 3 CLOSED

iex(5)> changeset = User.changeset(%User{}, %{name: "Klaus", avatar: remote_path})
** (EXIT from #PID<0.391.0>) an exception was raised:
    ** (UndefinedFunctionError) function nil.name/0 is undefined or private
        nil.name()
        (image) web/uploaders/avatar.ex:52: Image.Avatar.storage_dir/2
        lib/arc/storage/s3.ex:6: Arc.Storage.S3.put/3
        (elixir) lib/task/supervised.ex:85: Task.Supervised.do_apply/2
        (elixir) lib/task/supervised.ex:36: Task.Supervised.reply/5
        (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3

Interactive Elixir (1.4.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> [error] Task #PID<0.404.0> started from #PID<0.391.0> terminating
** (UndefinedFunctionError) function nil.name/0 is undefined (module nil is not available)
    nil.name()
    (image) web/uploaders/avatar.ex:52: Image.Avatar.storage_dir/2
    lib/arc/storage/s3.ex:6: Arc.Storage.S3.put/3
    (elixir) lib/task/supervised.ex:85: Task.Supervised.do_apply/2
    (elixir) lib/task/supervised.ex:36: Task.Supervised.reply/5
    (stdlib) proc_lib.erl:247: :proc_lib.init_p_do_apply/3
Function: #Function<0.124346436/0 in Arc.Actions.Store.async_put_version/3>
    Args: []

def transform(:medium, _) do
    {:convert, "-strip -thumbnail 600x600^ -gravity center -extent 600x600 -quality 85% -format png", :png}
  end

  def transform(:medium, _) do
    {:convert, "-strip -thumbnail 600x600^ -gravity center -extent 600x600 -format png", :png}
  end