Method find() bug in nested structure

[douglarek]

class EmployeeDocument(BaseDocument):
    __collection__ = 'employees'

    structure = {
        'name': unicode,
        'uid': basestring,
        'password': basestring,
        'hirer': {'name': unicode, 'token': basestring}
    }

Use find() to query, nothing found as this:

db.EmployeeDocument.find({'hirer': {'name': g.user, 'token': {'$exists': True}}})

but it works as this:

db.EmployeeDocument.find({'hirer': {'name': g.user, 'token': session.get('token')}})

Anything I missed ?