Fix failure when registering a user with no email when approval required

lib/pleroma/user.ex

@@ -905,7 +905,7 @@ defmodule Pleroma.User do
     end
   end
 
-  defp send_user_approval_email(user) do
+  defp send_user_approval_email(%User{email: email} = user) when is_binary(email) do
     user
     |> Pleroma.Emails.UserEmail.approval_pending_email()
     |> Pleroma.Emails.Mailer.deliver_async()
@@ -913,6 +913,10 @@ defmodule Pleroma.User do
     {:ok, :enqueued}
   end
 
+  defp send_user_approval_email(_user) do
+    {:ok, :skipped}
+  end
+
   defp send_admin_approval_emails(user) do
     all_superusers()
     |> Enum.filter(fn user -> not is_nil(user.email) end)

test/pleroma/user_test.exs

@@ -591,6 +591,21 @@ defmodule Pleroma.UserTest do
       refute_email_sent()
     end
 
+    test "it works when the registering user does not provide an email" do
+      clear_config([Pleroma.Emails.Mailer, :enabled], false)
+      clear_config([:instance, :account_activation_required], false)
+      clear_config([:instance, :account_approval_required], true)
+
+      cng = User.register_changeset(%User{}, @full_user_data |> Map.put(:email, ""))
+
+      # The user is still created
+      assert {:ok, %User{nickname: "nick"}} = User.register(cng)
+
+      # No emails are sent
+      ObanHelpers.perform_all()
+      refute_email_sent()
+    end
+
     test "it requires an email, name, nickname and password, bio is optional when account_activation_required is enabled" do
       clear_config([:instance, :account_activation_required], true)