Make sure activity recipient can't be nil

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/federation/activity_pub/publisher.ex

@@ -110,6 +110,9 @@ defmodule Mobilizon.Federation.ActivityPub.Publisher do
   @spec convert_followers_in_recipients(list(String.t())) :: {list(String.t()), list(String.t())}
   defp convert_followers_in_recipients(recipients) do
     Enum.reduce(recipients, {recipients, []}, fn recipient, {recipients, follower_actors} = acc ->
+      if is_nil(recipient) do
+        acc
+      else
         case Actors.get_actor_by_followers_url(recipient) do
           %Actor{} = group ->
             {Enum.filter(recipients, fn recipient -> recipient != group.followers_url end),
@@ -118,6 +121,7 @@ defmodule Mobilizon.Federation.ActivityPub.Publisher do
           nil ->
             acc
         end
+      end
     end)
   end
 
@@ -128,6 +132,9 @@ defmodule Mobilizon.Federation.ActivityPub.Publisher do
   @spec convert_members_in_recipients(list(String.t())) :: {list(String.t()), list(Actor.t())}
   defp convert_members_in_recipients(recipients) do
     Enum.reduce(recipients, {recipients, []}, fn recipient, {recipients, member_actors} = acc ->
+      if is_nil(recipient) do
+        acc
+      else
         case Actors.get_group_by_members_url(recipient) do
           # If the group is local just add external members
           %Actor{domain: domain} = group when is_nil(domain) ->
@@ -142,6 +149,7 @@ defmodule Mobilizon.Federation.ActivityPub.Publisher do
           _ ->
             acc
         end
+      end
     end)
   end
 end