diff --git a/mellon/adapters.py b/mellon/adapters.py
index a895892..3ff85c5 100644
--- a/mellon/adapters.py
+++ b/mellon/adapters.py
@@ -314,10 +314,7 @@ class DefaultAdapter(object):
         except User.DoesNotExist:
             pass
 
-        user = None
-        lookup_by_attributes = utils.get_setting(idp, 'LOOKUP_BY_ATTRIBUTES')
-        if lookup_by_attributes:
-            user = self._lookup_by_attributes(idp, saml_attributes, lookup_by_attributes)
+        user = self.lookup_by_attributes(idp, saml_attributes)
 
         created = False
         if not user:
@@ -343,6 +340,12 @@ class DefaultAdapter(object):
             logger.info('created new user %s with name_id %s from issuer %s', nameid_user, name_id, issuer)
         return nameid_user
 
+    def lookup_by_attributes(self, idp, saml_attributes):
+        rules = utils.get_setting(idp, 'LOOKUP_BY_ATTRIBUTES')
+        if rules:
+            return self._lookup_by_attributes(idp, saml_attributes, rules)
+        return None
+
     def _lookup_by_attributes(self, idp, saml_attributes, lookup_by_attributes):
         if not isinstance(lookup_by_attributes, list):
             logger.error('invalid LOOKUP_BY_ATTRIBUTES configuration %r: it must be a list', lookup_by_attributes)