如何避免使用GAE NDB返回None值？

Question

我有如下的复杂NDB查询：

employees = Employee.query(query.OR(Employee.passport_id == passport_id,
   Employee.inn == inn,
   query.AND(Employee.last_name == last_name,
    Employee.region == region,
    Employee.prof_area == prof_area),
   query.AND(Employee.last_name == last_name,
    Employee.first_name == first_name,
    Employee.date_of_birth == date_of_birth)
   ))

目前，当数据库值为None且我的值为None时，将返回此类实体。我怎么能避免这种情况？ 我想我可以做（像每个领域）：

if inn is None:
    inn = 'something-I-do-not-expect-in-database'

但它看起来不太好。