object: add helper functions to handle various forms of a given object and return a normalized one

lib/pleroma/object.ex

@@ -27,6 +27,10 @@ defmodule Pleroma.Object do
     Repo.one(from(object in Object, where: fragment("(?)->>'id' = ?", object.data, ^ap_id)))
   end
 
+  def normalize(obj) when is_map(obj), do: Object.get_by_ap_id(obj["id"])
+  def normalize(ap_id) when is_binary(ap_id), do: Object.get_by_ap_id(ap_id)
+  def normalize(_), do: nil
+
   def get_cached_by_ap_id(ap_id) do
     if Mix.env() == :test do
       get_by_ap_id(ap_id)

lib/pleroma/user.ex

@@ -458,7 +458,7 @@ defmodule Pleroma.User do
   end
 
   def get_notified_from_activity(%Activity{recipients: to, data: %{"type" => "Announce"} = data}) do
-    object = Object.get_by_ap_id(data["object"])
+    object = Object.normalize(data["object"])
 
     # ensure that the actor who published the announced object appears only once
     to =