Fix empty list handling in command map normalization

src/connection/mc_connection_man.erl

@@ -140,8 +140,10 @@ normalize_value({K, V}) when is_atom(K); is_binary(K) ->
 normalize_value(V) when is_map(V) ->
   %% Recursively normalize nested maps
   normalize_map_values(V);
+normalize_value([]) ->
+  [];
 normalize_value(V) when is_list(V) ->
-  %% Check if it's a proplist or just a list
+  %% Convert proplists to maps; regular lists keep BSON array semantics.
   case is_proplist(V) of
     true -> maps:from_list([{ensure_binary(K), normalize_value(Val)} || {K, Val} <- V]);
     false -> V  %% Regular list, leave as-is

test/tuple_normalization_SUITE.erl

@@ -16,6 +16,7 @@
   test_mixed_nested_structures/1,
   test_already_normalized_map/1,
   test_atom_keys_to_binary/1,
+  test_empty_list_unchanged/1,
   test_regular_list_unchanged/1,
   test_deep_nesting/1
 ]).
@@ -30,6 +31,7 @@ all() ->
     test_mixed_nested_structures,
     test_already_normalized_map,
     test_atom_keys_to_binary,
+    test_empty_list_unchanged,
     test_regular_list_unchanged,
     test_deep_nesting
   ].
@@ -146,6 +148,20 @@ test_atom_keys_to_binary(_Config) ->
   Result = normalize_map_values(Input),
   ?assertEqual(Expected, Result).
 
+test_empty_list_unchanged(_Config) ->
+  %% Empty lists should remain arrays, not be coerced into empty maps
+  Input = #{
+    <<"findAndModify">> => <<"devices">>,
+    <<"update">> => #{
+      <<"$set">> => #{
+        <<"test_3">> => []
+      }
+    }
+  },
+  Expected = Input,
+  Result = normalize_map_values(Input),
+  ?assertEqual(Expected, Result).
+
 test_regular_list_unchanged(_Config) ->
   %% Regular lists (not proplists) should remain unchanged
   Input = #{
@@ -172,4 +188,4 @@ test_deep_nesting(_Config) ->
     }
   },
   Result = normalize_map_values(Input),
-  ?assertEqual(Expected, Result).
+  ?assertEqual(Expected, Result).