Dict field in mongoengine does not save None types

When adding a new field to Dict type if the value is None key is never saved.
Attaching the code snippet below

import mongoengine
from mongoengine import *

class Test(Document):
    args = DictField()

test = Test(args={'hello': None})
test.save()
#create a new key count with None
test.args['count'] = None
test.save()
for item in Test.objects:
    print(item.args)

Output:

connected
{'hello': None}

Count with None is never saved !

But when doing this:

import mongoengine
from mongoengine import *

class Test(Document):
    args = DictField()

test = Test(args={'hello': None})
test.save()
test.args['count'] = '1'
test.save()
for item in Test.objects:
    print(item.args)

Output:

connected
{'hello': None, 'count': '1'}

When count is a non-None value it is saved

Start by running the provided Python reproduction with DictField and compare saving a newly added None value with a non-None value. Trace how the DictField contents are persisted during the second save. Done means a newly added key whose value is None is present after saving and reading the document again.