diff --git a/openwisp_controller/subnet_division/admin.py b/openwisp_controller/subnet_division/admin.py
index 131ae3076..b1182d501 100644
--- a/openwisp_controller/subnet_division/admin.py
+++ b/openwisp_controller/subnet_division/admin.py
@@ -32,8 +32,8 @@ class SubnetDivisionRuleInlineAdmin(
             '"Number of IPs" will not be possible.'
         ),
         'documentation_url': (
-            'https://github.com/openwisp/openwisp-controller'
-            '#limitations-of-subnet-division'
+            'https://openwisp.io/docs/dev/controller/user/subnet-division-rules.html'
+            '#limitations-of-subnet-division-rules'
         ),
     }
 
diff --git a/tests/openwisp2/sample_users/migrations/0001_initial.py b/tests/openwisp2/sample_users/migrations/0001_initial.py
index 2f74dbc9b..d3e08ab9d 100644
--- a/tests/openwisp2/sample_users/migrations/0001_initial.py
+++ b/tests/openwisp2/sample_users/migrations/0001_initial.py
@@ -262,7 +262,6 @@ class Migration(migrations.Migration):
                 ('url', models.URLField(blank=True, verbose_name='URL')),
             ],
             options={'abstract': False},
-            bases=(organizations.base.UnicodeMixin, models.Model),
         ),
         migrations.CreateModel(
             name='Group',
@@ -320,7 +319,6 @@ class Migration(migrations.Migration):
                 ),
             ],
             options={'abstract': False},
-            bases=(organizations.base.UnicodeMixin, models.Model),
         ),
         migrations.CreateModel(
             name='OrganizationOwner',
@@ -363,7 +361,6 @@ class Migration(migrations.Migration):
                 ),
             ],
             options={'abstract': False},
-            bases=(organizations.base.UnicodeMixin, models.Model),
         ),
         migrations.CreateModel(
             name='OrganizationInvitation',