Fix subscription banner on New Project page

Do not try to find `closest_gitlab_subscription` for projects that are
not persisted yet.

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/322546.

ee/app/helpers/ee/subscribable_banner_helper.rb

@@ -58,7 +58,9 @@ module EE
 
     def decorated_subscription
       entity = @project || @group
-      subscription = entity&.closest_gitlab_subscription
+      return unless entity && entity.persisted?
+
+      subscription = entity.closest_gitlab_subscription
 
       return unless subscription
 

ee/changelogs/unreleased/322546-fix-subscription-banner-for-new-project.yml

+---
+title: Fix subscription banner on New Project page
+merge_request: 56443
+author:
+type: fixed

ee/spec/helpers/ee/subscribable_banner_helper_spec.rb

@@ -3,6 +3,21 @@
 require 'spec_helper'
 
 RSpec.describe EE::SubscribableBannerHelper do
+  describe '#renew_subscription_path' do
+    it 'does not raise error if available project is not persisted' do
+      assign(:project, Project.new)
+
+      expect { helper.renew_subscription_path }.not_to raise_error
+    end
+
+    it 'does not raise error if entity is not available' do
+      assign(:project, nil)
+      assign(:group, nil)
+
+      expect { helper.renew_subscription_path }.not_to raise_error
+    end
+  end
+
   describe '#gitlab_subscription_or_license' do
     subject { helper.gitlab_subscription_or_license }