   end
 
   defp new_from_list([item | rest], acc) do
-    new_from_list(rest, [{item, []} | acc])
+    new_from_list(rest, [{item, @dummy_value} | acc])
   end
 
   defp new_from_list_transform([], _fun, acc) do
     :maps.from_list(acc)
   end
   defp new_from_list_transform([item | rest], fun, acc) do
-    new_from_list_transform(rest, fun, [{fun.(item), []} | acc])
+    new_from_list_transform(rest, fun, [{fun.(item), @dummy_value} | acc])
   end
 
   @doc """

  """
  @spec put(t(val), new_val) :: t(val | new_val) when val: value, new_val: value
  def put(%MapSet{map: map} = map_set, value) do
    %{map_set | map: Map.put(map, value, [])}
  end

  @doc """

      %{^key => _} ->
        filter_not_in(rest, map2, acc)
      _ ->
        filter_not_in(rest, map2, [{key, @dummy_value} | acc])
    end
  end

