FIX: if we have not target available do not redirect

app/controllers/application_controller.rb

@@ -222,7 +222,9 @@ class ApplicationController < ActionController::Base
       url = opts[:original_path] || request.fullpath
       permalink = Permalink.find_by_url(url)
 
-      if permalink.present?
+      # there are some cases where we have a permalink but no url
+      # cause category / topic was deleted
+      if permalink.present? && permalink.target_url
         # permalink present, redirect to that URL
         redirect_with_client_support permalink.target_url, status: :moved_permanently
         return

app/controllers/permalinks_controller.rb

@@ -8,9 +8,7 @@ class PermalinksController < ApplicationController
 
     raise Discourse::NotFound unless permalink
 
-    if permalink.external_url
-      redirect_to permalink.external_url, status: :moved_permanently
-    elsif permalink.target_url
+    if permalink.target_url
       redirect_to permalink.target_url, status: :moved_permanently
     else
       raise Discourse::NotFound

spec/requests/application_controller_spec.rb

@@ -18,6 +18,14 @@ RSpec.describe ApplicationController do
   describe 'build_not_found_page' do
     describe 'topic not found' do
 
+      it 'should not redirect to permalink if topic/category does not exist' do
+        topic = create_post.topic
+        Permalink.create!(url: topic.relative_url, topic_id: topic.id + 1)
+        topic.trash!
+        get topic.relative_url
+        expect(response.status).to eq(410)
+      end
+
       it 'should return permalink for deleted topics' do
         topic = create_post.topic
         external_url = 'https://somewhere.over.rainbow'