EnsureRePrepended: Don't break on chat messages.

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

@@ -27,7 +27,8 @@ def filter_by_summary(
 
   def filter_by_summary(_in_reply_to, child), do: child
 
-  def filter(%{"type" => "Create", "object" => child_object} = object) do
+  def filter(%{"type" => "Create", "object" => child_object} = object)
+      when is_map(child_object) do
     child =
       child_object["inReplyTo"]
       |> Object.normalize(child_object["inReplyTo"])

test/web/activity_pub/mrf/ensure_re_prepended_test.exs

@@ -78,5 +78,15 @@ test "it skip if parent and child summary isn't equal" do
       assert {:ok, res} = EnsureRePrepended.filter(message)
       assert res == message
     end
+
+    test "it skips if the object is only a reference" do
+      message = %{
+        "type" => "Create",
+        "object" => "somereference"
+      }
+
+      assert {:ok, res} = EnsureRePrepended.filter(message)
+      assert res == message
+    end
   end
 end