Django: filtering queryset by 'field__isnull=True' or 'field=None'?

I prefer the second solution which is handled better

Update

if value is None:
    filtered_queryset = queryset.filter(field__isnull=True)
    # Do some proessing with  filtered_queryset object with None values
else:
    filtered_queryset = queryset.filter(field=value)
    # Do some proessing with  filtered_queryset object with not NULL values

Query set can handle Null values..Based on this User.objects.filter(username=None) this would fetch only values where username=NULL

The ORM will handle None (cast it to NULL) for you and return a QuerySet object, so unless you need to catch None input the first example is fine.

>>> User.objects.filter(username=None)
[]
>>> type(_)
<class 'django.db.models.query.QuerySet'>
>>> str(User.objects.filter(username=None).query)
SELECT "auth_user"."id", "auth_user"."username", "auth_user"."first_name", "auth_user"."last_name", "auth_user"."email", "auth_user"."password", "auth_user"."is_staff", "auth_user"."is_active", "auth_user"."is_superuser", "auth_user"."last_login", "auth_user"."date_joined" FROM "auth_user" WHERE "auth_user"."username" IS NULL