fix: handle models with empty local_managers (#90)

* Fix value error

* test: add test for models with empty local_managers

* fix: check for local_managers being empty

Co-authored-by: Mike <22396211+Dresdn@users.noreply.github.com>

eav/registry.py

@@ -109,8 +109,13 @@ class Registry(object):
         # Save the old manager if the attribute name conflicts with the new one.
         if hasattr(self.model_cls, self.config_cls.manager_attr):
             mgr = getattr(self.model_cls, self.config_cls.manager_attr)
-            self.config_cls.old_mgr = mgr
-            self.model_cls._meta.local_managers.remove(mgr)
+
+            # For some models, `local_managers` may be empty, eg.
+            # django.contrib.auth.models.User and AbstractUser
+            if mgr in self.model_cls._meta.local_managers:
+                self.config_cls.old_mgr = mgr
+                self.model_cls._meta.local_managers.remove(mgr)
+
             self.model_cls._meta._expire_cache()
 
         # Attach the new manager to the model.

tests/test_registry.py

@@ -1,3 +1,4 @@
+from django.contrib.auth.models import User
 from django.test import TestCase
 
 import eav
@@ -100,3 +101,14 @@ class RegistryTests(TestCase):
             @eav.decorators.register_eav()
             class Foo(object):
                 pass
+
+    def test_model_without_local_managers(self):
+        """Test when a model doesn't have local_managers."""
+        # Check just in case test model changes in the future
+        assert bool(User._meta.local_managers) is False
+        eav.register(User)
+        assert isinstance(User.objects, eav.managers.EntityManager)
+
+        # Reverse check: managers should be empty again
+        eav.unregister(User)
+        assert bool(User._meta.local_managers) is False