Catch 404s.

lib/pleroma/web/static_fe/static_fe_controller.ex

@@ -61,7 +61,8 @@ def represent(%Activity{object: %Object{data: data}} = activity, selected) do
   end
 
   def show(%{assigns: %{notice_id: notice_id}} = conn, _params) do
-    activity = Activity.get_by_id_with_object(notice_id)
+    case Activity.get_by_id_with_object(notice_id) do
+      %Activity{} = activity ->
         timeline =
           activity.object.data["context"]
           |> ActivityPub.fetch_activities_for_context(%{})
@@ -69,11 +70,17 @@ def show(%{assigns: %{notice_id: notice_id}} = conn, _params) do
           |> Enum.map(&represent(&1, &1.object.id == activity.object.id))
 
         render(conn, "conversation.html", %{activities: timeline})
+
+      _ ->
+        conn
+        |> put_status(404)
+        |> render_error(:not_found, "Notice not found")
+    end
   end
 
   def show(%{assigns: %{username_or_id: username_or_id}} = conn, params) do
-    %User{} = user = User.get_cached_by_nickname_or_id(username_or_id)
-
+    case User.get_cached_by_nickname_or_id(username_or_id) do
+      %User{} = user ->
         timeline =
           ActivityPub.fetch_user_activities(user, nil, Map.take(params, @page_keys))
           |> Enum.map(&represent/1)
@@ -90,6 +97,12 @@ def show(%{assigns: %{username_or_id: username_or_id}} = conn, params) do
           prev_page_id: prev_page_id,
           next_page_id: next_page_id
         })
+
+      _ ->
+        conn
+        |> put_status(404)
+        |> render_error(:not_found, "User not found")
+    end
   end
 
   def assign_id(%{path_info: ["notice", notice_id]} = conn, _opts),