config: Fix showing the value of the default home page

Closes: #2314.

Tests:

- On a fresh testing container, verify that the file
/etc/apache2/conf-available/freedombox-apache-homepage.conf is not present.
Visit the config app and notice that home page shows as 'Apache Default'.

- Apply the patch and refresh the page. The page now shows 'FreedomBox
Service (Plinth)' as the home page.

- Functional tests work.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/config/__init__.py

@@ -105,6 +105,12 @@ def get_hostname():
 
 def home_page_url2scid(url):
     """Return the shortcut ID of the given home page url."""
+    # url is None when the freedombox-apache-homepage configuration file does
+    # not exist. In this case, the default redirect in /plinth from the shipped
+    # configuration file is effective.
+    if url is None:
+        return 'plinth'
+
     if url in ('/plinth/', '/plinth', 'plinth'):
         return 'plinth'
 

plinth/modules/config/tests/test_config.py

@@ -76,7 +76,7 @@ def test_domainname_field():
 def test_homepage_mapping():
     """Basic tests for homepage functions."""
     func = home_page_url2scid
-    assert func(None) is None
+    assert func(None) == 'plinth'
     assert func('/unknown/url') is None
     assert func('/plinth/') == 'plinth'
     assert func('/plinth') == 'plinth'