Changing default slug causes get_site to return no pages.

[kimberlyherman]

Issue Summary

When we change the slug for a page, the get_url_paths method (called by get_site) in the Page class returns no pages

Steps to Reproduce

1. Start a new project with wagtail start myproject
2. Set up a basic content site_ with a few index child pages or use an existing demo built on Wagtail 2.16 that has child pages and the Promote tab in the admin parent page
3. Add this method to the BlogIndexPage in models.py to get all child pages
   def get_collections():
res = None
site = self.get_site()
if site:
res = res.in_site(site)
return res
4. in your index template add this not pretty, but enough to show the data
   <div> {% page.get_collections %}</div>
5. run your site and go to the Promote tab on the index page
6. change the slug, save draft, publish
7. refresh the index page and see that the data is gone

I expected all results for get_site

Technical details

• Python version: 3.8
• Django version: 2.2
• Wagtail version: 2.16
• Browser version: Chrome 108

[NXPY123]

@kimberlyherman Can you specify the steps better? I'm having trouble reproducing the issue

[gasman]

The code snippet above looks incorrect to me - if site is defined, then the line res = res.in_site(site) will attempt to call in_site on None.

[gasman]

Closing due to lack of updates (and Wagtail 2.16 is well out of support now).