Fix age_at method

aleksis/core/models.py

@@ -181,12 +181,13 @@ class Person(ExtensibleModel):
         return self.age_at(timezone.datetime.now().date())
 
     def age_at(self, today):
-        years = today.year - self.date_of_birth.year
-        if (self.date_of_birth.month > today.month
-            or (self.date_of_birth.month == today.month
-                and self.date_of_birth.day > today.day)):
-            years -= 1
-        return years
+        if self.date_of_birth:
+            years = today.year - self.date_of_birth.year
+            if (self.date_of_birth.month > today.month
+                or (self.date_of_birth.month == today.month
+                    and self.date_of_birth.day > today.day)):
+                years -= 1
+            return years
 
     def save(self, *args, **kwargs):
         super().save(*args, **kwargs)