Check for None on real_model in get_real_instance

polymorphic/models.py

@@ -157,6 +157,10 @@ def get_real_instance(self):
         retrieve objects, then the complete object with it's real class/type
         and all fields may be retrieved with this method.
 
+        If the model of the object's actual type does not exist (i.e. its
+        ContentType is stale), this method raises a
+        :class:`~polymorphic.models.PolymorphicTypeInvalid` exception.
+
         .. note::
             Each method call executes one db query (if necessary).
             Use the :meth:`~polymorphic.managers.PolymorphicQuerySet.get_real_instances`
@@ -165,6 +169,11 @@ def get_real_instance(self):
         real_model = self.get_real_instance_class()
         if real_model == self.__class__:
             return self
+        if real_model is None:
+            raise PolymorphicTypeInvalid(
+                f"ContentType {self.polymorphic_ctype_id} for {self.__class__} "
+                f"#{self.pk} does not have a corresponding model!"
+            )
         return real_model.objects.db_manager(self._state.db).get(pk=self.pk)
 
     def __init__(self, *args, **kwargs):

polymorphic/tests/test_orm.py

@@ -321,6 +321,15 @@ def test_manual_get_real_instance(self):
         o = Model2A.objects.non_polymorphic().get(field1="C1")
         assert o.get_real_instance().__class__ == Model2C
 
+    def test_get_real_instance_with_stale_content_type(self):
+        ctype = ContentType.objects.create(app_label="tests", model="stale")
+        o = Model2A.objects.create(field1="A1", polymorphic_ctype=ctype)
+
+        assert o.get_real_instance_class() is None
+        match = "does not have a corresponding model"
+        with pytest.raises(PolymorphicTypeInvalid, match=match):
+            o.get_real_instance()
+
     def test_non_polymorphic(self):
         self.create_model2abcd()