google-app-engine - 如何避免使用 GAE NDB 返回 None 值？

Question

我有如下复杂的 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)
   ))

当前，当数据库值为None且我的值为时None，将返回此类实体。我怎样才能避免这种情况？我想我可以做类似的事情（对于每个领域）：

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

但它看起来不是很好。