Notifications: Never return `nil` in the notification list.

lib/pleroma/notification.ex

@@ -367,6 +367,7 @@ defmodule Pleroma.Notification do
         do_send = do_send && user in enabled_receivers
         create_notification(activity, user, do_send)
       end)
+      |> Enum.filter(& &1)
 
     {:ok, notifications}
   end

test/notification_test.exs

@@ -21,7 +21,19 @@ defmodule Pleroma.NotificationTest do
   alias Pleroma.Web.Push
   alias Pleroma.Web.Streamer
 
+  # TODO: Test there's no nil notifications
+
   describe "create_notifications" do
+    test "never returns nil" do
+      user = insert(:user)
+      other_user = insert(:user, %{invisible: true})
+
+      {:ok, activity} = CommonAPI.post(user, %{status: "yeah"})
+      {:ok, activity} = CommonAPI.react_with_emoji(activity.id, other_user, "☕")
+
+      refute {:ok, [nil]} == Notification.create_notifications(activity)
+    end
+
     test "creates a notification for an emoji reaction" do
       user = insert(:user)
       other_user = insert(:user)