Fix module attribute with empty list in Macro.to_string, closes #12097

Author: josevalim

lib/elixir/lib/code/normalizer.ex

@@ -201,7 +201,7 @@ defmodule Code.Normalizer do
   defp do_normalize({:@, meta, [{name, name_meta, [value]}]}, state) do
     value =
       cond do
-        keyword?(value) ->
+        keyword?(value) and value != [] ->
           normalize_kw_args(value, state, true)
 
         is_list(value) ->

lib/elixir/test/elixir/code_normalizer/quoted_ast_test.exs

@@ -544,6 +544,12 @@ defmodule Code.Normalizer.QuotedASTTest do
     end
 
     test "list in module attribute" do
+      assert quoted_to_string(
+               quote do
+                 @foo []
+               end
+             ) == "@foo []"
+
       assert quoted_to_string(
                quote do
                  @foo [1]