MRF Object Age Policy: Don't break on messages without cc/to

lib/pleroma/web/activity_pub/mrf/object_age_policy.ex

@@ -37,8 +37,13 @@ defp check_reject(message, actions) do
   defp check_delist(message, actions) do
     if :delist in actions do
       with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
-        to = List.delete(message["to"], Pleroma.Constants.as_public()) ++ [user.follower_address]
-        cc = List.delete(message["cc"], user.follower_address) ++ [Pleroma.Constants.as_public()]
+        to =
+          List.delete(message["to"] || [], Pleroma.Constants.as_public()) ++
+            [user.follower_address]
+
+        cc =
+          List.delete(message["cc"] || [], user.follower_address) ++
+            [Pleroma.Constants.as_public()]
 
         message =
           message
@@ -58,8 +63,8 @@ defp check_delist(message, actions) do
   defp check_strip_followers(message, actions) do
     if :strip_followers in actions do
       with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
-        to = List.delete(message["to"], user.follower_address)
-        cc = List.delete(message["cc"], user.follower_address)
+        to = List.delete(message["to"] || [], user.follower_address)
+        cc = List.delete(message["cc"] || [], user.follower_address)
 
         message =
           message

test/web/activity_pub/mrf/object_age_policy_test.exs

@@ -38,6 +38,17 @@ defp get_new_message do
   end
 
   describe "with reject action" do
+    test "works with objects with empty to or cc fields" do
+      Config.put([:mrf_object_age, :actions], [:reject])
+
+      data =
+        get_old_message()
+        |> Map.put("cc", nil)
+        |> Map.put("to", nil)
+
+      assert match?({:reject, _}, ObjectAgePolicy.filter(data))
+    end
+
     test "it rejects an old post" do
       Config.put([:mrf_object_age, :actions], [:reject])
 
@@ -56,6 +67,21 @@ test "it allows a new post" do
   end
 
   describe "with delist action" do
+    test "works with objects with empty to or cc fields" do
+      Config.put([:mrf_object_age, :actions], [:delist])
+
+      data =
+        get_old_message()
+        |> Map.put("cc", nil)
+        |> Map.put("to", nil)
+
+      {:ok, _u} = User.get_or_fetch_by_ap_id(data["actor"])
+
+      {:ok, data} = ObjectAgePolicy.filter(data)
+
+      assert Visibility.get_visibility(%{data: data}) == "unlisted"
+    end
+
     test "it delists an old post" do
       Config.put([:mrf_object_age, :actions], [:delist])
 
@@ -80,6 +106,22 @@ test "it allows a new post" do
   end
 
   describe "with strip_followers action" do
+    test "works with objects with empty to or cc fields" do
+      Config.put([:mrf_object_age, :actions], [:strip_followers])
+
+      data =
+        get_old_message()
+        |> Map.put("cc", nil)
+        |> Map.put("to", nil)
+
+      {:ok, user} = User.get_or_fetch_by_ap_id(data["actor"])
+
+      {:ok, data} = ObjectAgePolicy.filter(data)
+
+      refute user.follower_address in data["to"]
+      refute user.follower_address in data["cc"]
+    end
+
     test "it strips followers collections from an old post" do
       Config.put([:mrf_object_age, :actions], [:strip_followers])