FIX: error when group_in_subject enabled but no group in pm

app/mailers/user_notifications.rb

@@ -435,13 +435,11 @@ class UserNotifications < ActionMailer::Base
 
     if post.topic.private_message?
       subject_pm =
-        if opts[:show_group_in_subject]
-          if group = post.topic.allowed_groups&.first
-            if group.full_name
-              "[#{group.full_name}] "
-            else
-              "[#{group.name}] "
-            end
+        if opts[:show_group_in_subject] and group = post.topic.allowed_groups&.first
+          if group.full_name
+            "[#{group.full_name}] "
+          else
+            "[#{group.name}] "
           end
         else
           I18n.t('subject_pm')

spec/mailers/user_notifications_spec.rb

@@ -467,6 +467,12 @@ describe UserNotifications do
 
         include_examples "includes first group name"
       end
+
+      context "no groups in pm" do
+        it "includes %{optional_pm} in subject" do
+          expect(mail.subject).to include("[PM] ")
+        end
+      end
     end
   end