djangocms-page-sitemap breaks django-cms page types display

[fp4code]

Description

After 'djangocms_page_sitemap' is added to INSTALLED_APPS,
page types cannot be displayed

Steps to reproduce

1. Install a django-cms site

python3 -m venv env
pip install --upgrade pip
pip install wheel
. env/bin/activate
pip install --upgrade pip
pip install wheel
pip install djangocms-installer
djangocms --django-version 2.2 mysite # same problem with 3.1
pip install djangocms-page-sitemap
cd mysite/
./manage.py runserver

2. Connect as admin/admin
3. Add a home page
4. Add the page type "Type 1" with slug "type1"
5. Display http://localhost:8000/en/page_types/type-1/

That's OK. Now:

6. Edit mysite/settings.py to add 'djangocms-page-sitemap' to INSTALLED_APPS
7. Migrate and start server

./manage.py migrate
./manage.py runserver

8. Try to display the page type http://localhost:8000/en/page_types/type-1/

TypeError at /en/page_types/type-1/

Versions

Python 3.8.6, Django==2.2.18, django-cms==3.8.0, djangocms-page-sitemap==1.0.0

Actual behaviour

Internal Server Error: /en/page_types/type-1/
Traceback (most recent call last):
  File "django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "django/core/handlers/base.py", line 145, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "django/core/handlers/base.py", line 143, in _get_response
    response = response.render()
  File "django/template/response.py", line 106, in render
    self.content = self.rendered_content
  File "/django/template/response.py", line 83, in rendered_content
    content = template.render(context, self._request)
  File "django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "django/template/base.py", line 171, in render
    return self._render(context)
  File "django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 163, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "classytags/core.py", line 151, in render
    return self.render_tag(context, **kwargs)
  File "sekizai/templatetags/sekizai_tags.py", line 87, in render_tag
    rendered_contents = nodelist.render(context)
  File "django/template/base.py", line 937, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 904, in render_annotated
    return self.render(context)
  File "classytags/core.py", line 151, in render
    return self.render_tag(context, **kwargs)
  File "cms/templatetags/cms_tags.py", line 443, in render_tag
    return toolbar.render_with_structure(context, nodelist)
  File "cms/toolbar/toolbar.py", line 467, in render_with_structure
    self.populate()
  File "cms/toolbar/toolbar.py", line 407, in populate
    self._call_toolbar('populate')
  File "cms/toolbar/toolbar.py", line 434, in _call_toolbar
    getattr(toolbar, func_name)()
  File "djangocms_page_sitemap/cms_toolbars.py", line 37, in populate
    position = current_page_menu.find_first(Break, identifier=PAGE_MENU_THIRD_BREAK) - 1
TypeError: unsupported operand type(s) for -: 'NoneType' and 'int'
[11/Feb/2021 16:02:06] "GET /en/page_types/type-1/ HTTP/1.1" 500 168859

[yakky]

@fp4code thanks for reporting this issue. It's been fixed with #76 and it will be released soon