Can not upsert when has field named 'id'

When upserting a document, if there's a field named id, error happened.

~/test.py in <module>
     11 connect(db='test1', host='127.0.0.1', port=27017)
     12 
---> 13 A.objects(x=1).upsert_one(id=1)

/usr/local/var/pyenv/versions/3.6.6/envs/one/lib/python3.6/site-packages/mongoengine/queryset/base.py in upsert_one(self, write_concern, **update)
    562 
    563         if atomic_update.raw_result['updatedExisting']:
--> 564             document = self.get()
    565         else:
    566             document = self._document.objects.with_id(atomic_update.upserted_id)

/usr/local/var/pyenv/versions/3.6.6/envs/one/lib/python3.6/site-packages/mongoengine/queryset/base.py in get(self, *q_objs, **query)
    270 
    271         try:
--> 272             result = next(queryset)
    273         except StopIteration:
    274             msg = ('%s matching query does not exist.'

/usr/local/var/pyenv/versions/3.6.6/envs/one/lib/python3.6/site-packages/mongoengine/queryset/base.py in __next__(self)
   1491         doc = self._document._from_son(
   1492             raw_doc, _auto_dereference=self._auto_dereference,
-> 1493             only_fields=self.only_fields)
   1494 
   1495         if self._scalar:

/usr/local/var/pyenv/versions/3.6.6/envs/one/lib/python3.6/site-packages/mongoengine/base/document.py in _from_son(cls, son, _auto_dereference, only_fields, created)
    720             data = {k: v for k, v in data.items() if k in cls._fields}
    721 
--> 722         obj = cls(__auto_convert=False, _created=created, __only_fields=only_fields, **data)
    723         obj._changed_fields = changed_fields
    724         if not _auto_dereference:

/usr/local/var/pyenv/versions/3.6.6/envs/one/lib/python3.6/site-packages/mongoengine/base/document.py in __init__(self, *args, **values)
     76                     'The fields "{0}" do not exist on the document "{1}"'
     77                 ).format(_undefined_fields, self._class_name)
---> 78                 raise FieldDoesNotExist(msg)
     79 
     80         if self.STRICT and not self._dynamic:

FieldDoesNotExist: The fields "{'_id'}" do not exist on the document "A"

I guess a field named id should be fine since I see example like

user = User.objects.get(id=user_id)
user.switch_db('archive-db')
user.save()

in the document.

from mongoengine import IntField, Document, connect


class A(Document):
    x = IntField()
    id = IntField()


connect(db='test1', host='127.0.0.1', port=27017)

A.objects(x=1).upsert_one(id=1)  # <A: A object>
A.objects(x=1).upsert_one(id=1)  # Error

Reproduce the two calls in test.py and start by reading mongoengine/queryset/base.py around upsert_one, then follow the document construction path in mongoengine/base/document.py. Confirm that a document with an id field can be upserted repeatedly without FieldDoesNotExist for _id, and add or run regression coverage for both calls.