Unable to use next() in gremlin-python

# Python 3.10.12
# janusgraph 1.0.0
# gremlinpython==3.7.0

from gremlin_python.process.anonymous_traversal import traversal
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection

connection = DriverRemoteConnection("ws://jgserver:8182/gremlin", "g")
g = traversal().withRemote(connection)

g.V().drop().iterate()
g.E().drop().iterate()
v1 = g.addV('vertex').property('name', 'v1').next()

[...]

~/.local/lib/python3.10/site-packages/gremlin_python/structure/io/graphbinaryV1.py in read_object(self, b)
    192             return self.to_object(io.BytesIO(b))
    193         elif isinstance(b, io.BufferedIOBase):
--> 194             return self.to_object(b)
    195 
    196     def to_object(self, buff, data_type=None, nullable=True):

~/.local/lib/python3.10/site-packages/gremlin_python/structure/io/graphbinaryV1.py in to_object(self, buff, data_type, nullable)
    201                     buff.read(1)
    202                 return None
--> 203             return self.deserializers[DataType(bt)].objectify(buff, self, nullable)
    204         else:
    205             return self.deserializers[data_type].objectify(buff, self, nullable)

KeyError: <DataType.custom: 0>