bson.errors.InvalidDocument: cannot encode object: frozenset()/set()

[art049]

Exception while saving an object containing either a frozenset or a set:

from odmantic import Model, AIOEngine
from odmantic.bson import ObjectId

class UserModel(Model):
    username: str
    favorites_article_ids: FrozenSet[ObjectId] = frozenset()

engine = AIOEngine()
await engine.save(UserModel(username="jean"))