Fix error when using `date_hierarchy` field in the admin

Closes: #201
2016-03-11 17:13:09 +01:00 · 2016-03-11 17:13:09 +01:00 · 88922d7d5e
parent 6319dabcef
commit 88922d7d5e
1 changed files with 2 additions and 1 deletions
--- a/polymorphic/query.py
+++ b/polymorphic/query.py
@ -194,6 +194,7 @@ class PolymorphicQuerySet(QuerySet):
                translate_polymorphic_Q_object(self.model, a)
            elif hasattr(a, 'get_source_expressions'):
                for source_expression in a.get_source_expressions():
+                    if source_expression is not None:
                        patch_lookup_gte_18(source_expression)
            else:
                a.name = translate_polymorphic_field_path(self.model, a.name)