fields not working properly

code segment

class SectorMapping(DynamicDocument):
    date = DynamicField()
    concept = DynamicField()
    sub_concepts = DynamicField(default=[])
    type = DynamicField()  
    end_date = DynamicField() 

    meta = {
        'indexes': [
            {
                'fields': ['date', 'concept'],
                'unique': True
            },
            {
                'fields': ['date']
            }
        ],
        'db_alias': 'hunter',
        'collection': 'sector_mapping'
    }
sm = SectorMapping.objects.fields(_id=0, date=1, sub_concepts=0).first()

print(sm.to_mongo().to_dict())

output

{'date': datetime.datetime(2018, 9, 12, 0, 0), 'sub_concepts': []}

issue

I set the fields sub_concepts=0, but I got sub_concepts returned. Seems something wrong

version

mongoengine 0.15.3

Start by reproducing the provided SectorMapping example with MongoEngine 0.15.3 and inspect how DynamicDocument.fields() handles the projection. Confirm the expected result is that sub_concepts is omitted from sm.to_mongo().to_dict() when requested with sub_concepts=0.