Gremlin.net throwing exception when using tree

Question

When using the following query in Gremlin.net, I get the exception: System.Collections.Generic.KeyNotFoundException: 'The given key 'DataType{ TypeCode = 43 }' was not present in the dictionary.'

var result = g
  .V()
  .Repeat(OutE("composed-of").InV().SimplePath())
  .Tree<object>()
  .Promise<dynamic>(t => t.ToList());

Server is running from docker:

- services
    gramling_server:
      image: tinkerpop/gremlin-server
      restart: always
      platform: linux/x86_64
      ports:
        - "8182:8182"
      volumes:
        - tinkerpop_data_container:/data

UPDATE:

I changed the messageSerializer on the GremlinClient class to GraphSON3MessageSerializer and get the following error. Deserializer for "g:Tree" not found.
My guess is "TypeCode 43" is this g:Tree