Try to handle misconfiguration scenarios gracefully

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

@@ -1,16 +1,32 @@
 defmodule Pleroma.Web.ActivityPub.MRF.FollowBotPolicy do
   @behaviour Pleroma.Web.ActivityPub.MRF
+  alias Pleroma.Config
   alias Pleroma.User
   alias Pleroma.Web.CommonAPI
   require Logger
 
   @impl true
   def filter(message) do
-    Task.start(fn ->
-      follower_nickname = Pleroma.Config.get([:mrf_follow_bot, :follower_nickname])
-
-      with %User{} = follower <- User.get_cached_by_nickname(follower_nickname),
+    with follower_nickname <- Config.get([:mrf_follow_bot, :follower_nickname]),
+         %User{} = follower <- User.get_cached_by_nickname(follower_nickname),
          %{"type" => "Create", "object" => %{"type" => "Note"}} <- message do
+      try_follow(follower, message)
+    else
+      nil ->
+        Logger.warn(
+          "#{__MODULE__} skipped because of missing :mrf_follow_bot, :follower_nickname configuration or the account
+            does not exist."
+        )
+
+        {:ok, message}
+
+      _ ->
+        {:ok, message}
+    end
+  end
+
+  defp try_follow(follower, message) do
+    Task.start(fn ->
       to = Map.get(message, "to", [])
       cc = Map.get(message, "cc", [])
       actor = [message["actor"]]
@@ -28,7 +44,6 @@ def filter(message) do
           CommonAPI.follow(follower, user)
         end
       end)
-      end
     end)
 
     {:ok, message}