Fixes #3794 - Example payload in webhook view leads to 500 error

app/controllers/webhooks_controller.rb

@@ -4,9 +4,7 @@ class WebhooksController < ApplicationController
   prepend_before_action { authentication_check && authorize! }
 
   def preview
-    access_condition = Ticket.access_condition(current_user, 'read')
-
-    ticket = Ticket.where(access_condition).last
+    ticket = TicketPolicy::ReadScope.new(current_user).resolve.last
 
     render json:   JSON.pretty_generate({
                                           ticket:  TriggerWebhookJob::RecordPayload.generate(ticket),

spec/system/manage/webhooks_spec.rb

@@ -3,7 +3,23 @@
 require 'rails_helper'
 
 RSpec.describe 'Manage > Webhook', type: :system do
-  context 'deleting' do
+
+  context 'when showing the example payload' do
+
+    it 'shows correctly' do
+      visit '/#manage/webhook'
+
+      within :active_content do
+        click 'a[data-type="payload"]'
+      end
+
+      in_modal disappears: false do
+        expect(page).to have_text('X-Zammad-Trigger:')
+      end
+    end
+  end
+
+  context 'when deleting' do
     let!(:webhook) { create(:webhook) }
     let!(:trigger) { create(:trigger, perform: { 'notification.webhook' => { 'webhook_id' => webhook.id.to_s } }) }