How to use the pony.orm.Optional function in pony

def define_binding(db):
    class ChannelPeer(db.Entity):
        """
        This binding stores public keys of IPv8 peers that sent us some GigaChannel data. It is used by the
        voting system.
        """

        rowid = orm.PrimaryKey(int, size=64, auto=True)
        public_key = orm.Required(database_blob, unique=True)
        individual_votes = orm.Set("ChannelVote", reverse='voter')
        added_on = orm.Optional(datetime, default=datetime.utcnow)

    return ChannelPeer

name = orm.PrimaryKey(str)
        display_name = orm.Optional(str)
        description = orm.Optional(str, nullable=True)
        created_at = orm.Required(datetime, default=datetime.now())
        metadata = orm.Optional(orm.Json, nullable=True)
        updated_at = orm.Optional(datetime)

        # dataset - metadata
        parameter = orm.Optional(orm.Json, nullable=True)
        unit = orm.Optional(str)
        datatype = orm.Optional(str)
        file_format = orm.Optional(str)
        source = orm.Optional(str)
        options = orm.Optional(orm.Json, nullable=True)
        status = orm.Optional(str)
        message = orm.Optional(str)
        file_path = orm.Optional(str, nullable=True)
        visualization_path = orm.Optional(str)

        # setup relationships
        collection = orm.Required(Collection)
        catalog_entry = orm.Required(str)

    class Providers(db.Entity):
        provider = orm.PrimaryKey(str)
        username = orm.Required(str)
        password = orm.Required(str)

    class QuestCatalog(db.Entity):
        service_id = orm.PrimaryKey(str)
        created_at = orm.Required(datetime, default=datetime.now())
        updated_at = orm.Optional(datetime)

# setup relationships
        datasets = orm.Set('Dataset')

    class Dataset(db.Entity):
        name = orm.PrimaryKey(str)
        display_name = orm.Optional(str)
        description = orm.Optional(str, nullable=True)
        created_at = orm.Required(datetime, default=datetime.now())
        metadata = orm.Optional(orm.Json, nullable=True)
        updated_at = orm.Optional(datetime)

        # dataset - metadata
        parameter = orm.Optional(orm.Json, nullable=True)
        unit = orm.Optional(str)
        datatype = orm.Optional(str)
        file_format = orm.Optional(str)
        source = orm.Optional(str)
        options = orm.Optional(orm.Json, nullable=True)
        status = orm.Optional(str)
        message = orm.Optional(str)
        file_path = orm.Optional(str, nullable=True)
        visualization_path = orm.Optional(str)

        # setup relationships
        collection = orm.Required(Collection)
        catalog_entry = orm.Required(str)

    class Providers(db.Entity):
        provider = orm.PrimaryKey(str)
        username = orm.Required(str)
        password = orm.Required(str)

user_id = orm.Required(int, default=1)

    name = orm.Required(unicode, 80, unique=True)
    urlname = orm.Required(unicode, 80, unique=True)

    topic_count = orm.Required(int, default=0)
    follow_count = orm.Required(int, default=0)
    role = orm.Required(unicode, 10, default='node')

    created_at = orm.Required(int, default=int(time.time()))
    updated_at = orm.Required(int, default=int(time.time()))
    active = orm.Required(int, default=int(time.time()))

    description = orm.Optional(orm.LongUnicode)
    summary = orm.Optional(orm.LongUnicode)
    style = orm.Optional(unicode, 6000)

    icon_img = orm.Optional(unicode, 400)
    head_img = orm.Optional(unicode, 400)
    background_img = orm.Optional(unicode, 400)

    @property
    def url(self):
        return '/node/' + self.urlname

    @property
    def icon(self):
        if self.icon_img:
            return self.icon_img
        else:
            return config.node_icon_url

"""
        This ORM binding represents Channel entries in the GigaChannel system. Each channel is a Collection that
        additionally has Torrent properties, such as infohash, etc. The torrent properties are used to associate
        a torrent that holds the contents of the channel dumped on the disk in the serialized form.
        Methods for committing channels into the torrent form are implemented in this class.
        """

        _discriminator_ = CHANNEL_TORRENT

        # Serializable
        start_timestamp = orm.Optional(int, size=64, default=0)

        # Local
        subscribed = orm.Optional(bool, default=False, index=True)
        share = orm.Optional(bool, default=False, index=True)
        votes = orm.Optional(float, default=0.0, index=True)
        individual_votes = orm.Set("ChannelVote", reverse="channel")
        local_version = orm.Optional(int, size=64, default=0)

        votes_scaling = 1.0

        # Special class-level properties
        _payload_class = ChannelMetadataPayload
        _channels_dir = None
        _category_filter = None
        _CHUNK_SIZE_LIMIT = 1 * 1024 * 1024  # We use 1MB chunks as a workaround for Python's lack of string pointers
        payload_arguments = _payload_class.__init__.__code__.co_varnames[
            : _payload_class.__init__.__code__.co_argcount
        ][1:]

        # As channel metadata depends on the public key, we can't include the infohash in nonpersonal_attributes
        nonpersonal_attributes = set(db.CollectionNode.nonpersonal_attributes)

class Collection(db.Entity):
        name = orm.PrimaryKey(str)
        display_name = orm.Optional(str)
        description = orm.Optional(str)
        created_at = orm.Required(datetime, default=datetime.now())
        updated_at = orm.Optional(datetime)
        metadata = orm.Optional(orm.Json, nullable=True)

        # setup relationships
        datasets = orm.Set('Dataset')

    class Dataset(db.Entity):
        name = orm.PrimaryKey(str)
        display_name = orm.Optional(str)
        description = orm.Optional(str, nullable=True)
        created_at = orm.Required(datetime, default=datetime.now())
        metadata = orm.Optional(orm.Json, nullable=True)
        updated_at = orm.Optional(datetime)

        # dataset - metadata
        parameter = orm.Optional(orm.Json, nullable=True)
        unit = orm.Optional(str)
        datatype = orm.Optional(str)
        file_format = orm.Optional(str)
        source = orm.Optional(str)
        options = orm.Optional(orm.Json, nullable=True)
        status = orm.Optional(str)
        message = orm.Optional(str)
        file_path = orm.Optional(str, nullable=True)
        visualization_path = orm.Optional(str)

class Image(db.Entity):
    _table_ = "images"
    REGULAR = 1080
    SMALL = 400
    THUMB = 200
    url = PrimaryKey(str)
    height = Optional(int)
    width = Optional(int)
    color = Optional(str, sql_default="''")
    playlist = Optional("Playlist")
    artist = Optional("Artist")
    genre = Optional("Genre")
    country = Optional("Country")
    city = Optional("City")
    user = Optional("User")
    unsplash_id = Optional(str, index=True, sql_default="''")
    unsplash_user_fullname = Optional(str, sql_default="''")
    unsplash_user_username = Optional(str, sql_default="''")

    # pylint: disable=no-self-use

    @classmethod
    def unsplash_url(cls):
        return f"https://unsplash.com/?utm_source={config.unsplash.app_name}&utm_medium=referral"

    @classmethod
    def unsplash_user_url(cls, username):
        return f"https://unsplash.com/@{username}?utm_source={config.unsplash.app_name}&utm_medium=referral"

    @classmethod
    def unsplash_credits(cls, user_fullname, username):

col_float3 = Required(float, default=2.2)
        col_smallint3 = Required(int, size=16, default=2)
        col_int3 = Required(int, size=32, default=2000000)
        col_bigint3 = Required(int, size=64, default=99999999)
        col_char3 = Required(str, max_len=255, default='value1')
        col_text3 = Required(LongUnicode, default='Moo,Foo,Baa,Waa,Moo,Foo,Baa,Waa,Moo,Foo,Baa,Waa')
        col_decimal3 = Required(Decimal, 12, 8, default=Decimal('2.2'))
        col_json3 = Required(Json, default={'a':1, 'b':'b', 'c':[2], 'd':{'e': 3}, 'f': True})

        col_float4 = Optional(float)
        col_smallint4 = Optional(int, size=16)
        col_int4 = Optional(int, size=32)
        col_bigint4 = Optional(int, size=64)
        col_char4 = Optional(str, max_len=255)
        col_text4 = Optional(LongUnicode)
        col_decimal4 = Optional(Decimal, 12, 8)
        col_json4 = Optional(Json)


dbtype = os.environ.get('DBTYPE', '')
if dbtype == 'postgres':
    db.bind(provider='postgres', user='postgres', password=None, host='127.0.0.1', database='tbench')
elif dbtype == 'mysql':
    db.bind(provider='mysql', host='127.0.0.1', user='root', passwd='', db='tbench')
else:
    db.bind(provider='sqlite', filename='/dev/shm/db.sqlite3', create_db=True)

db.generate_mapping(create_tables=True)

YEAR = 6
        ALL = 7
        INTRO = 8

    id = PrimaryKey(str)  # pylint: disable=redefined-builtin
    collaborative = Required(bool)
    name = Required(str)
    description = Optional(str, sql_default="''")
    owner = Required(SpotifyUser)
    public = Required(bool)
    snapshot_id = Required(str)
    tracks = Required(int)
    popularity = Optional(int, index=True, sql_default="0")
    genre = Optional(Genre)
    country = Optional(Country)
    city = Optional(City)
    date = Optional(date, index=True)
    year = Optional(int)
    women = Optional(bool, index=True, sql_default=SQL_DEFAULT.bool_false)
    christmas = Optional(bool, index=True, sql_default=SQL_DEFAULT.bool_false)
    meta = Optional(bool, index=True, sql_default=SQL_DEFAULT.bool_false)
    images = Set(Image, cascade_delete=True)

    def play(self, client, device=None):
        return client.start_playback(playlist=self.uri, device=device)

    @property
    def uri(self):
        return f"spotify:user:{self.owner.id}:playlist:{self.id}"

    @property
    def href(self):

# coding: utf-8

import time
from pony import orm
from ._base import db, BaseModel
from collipa import config


class Collect(db.Entity, BaseModel):
    user_id = orm.Required(int)

    created_at = orm.Required(int, default=int(time.time()))

    collect_class_id = orm.Optional(int)
    topic_id = orm.Optional(int)
    reply_id = orm.Optional(int)
    tweet_id = orm.Optional(int)

    content = orm.Optional(orm.LongUnicode)

    def __str__(self):
        return self.id

    def __repr__(self):
        return '' % self.id

    def save(self):
        now = int(time.time())
        self.created_at = now

        if self.topic_id: