_state__internal__

[rpammeraal]

AM trying to create a resource class as stated in documentation at https://docs.dagster.io/concepts/resources. Class looks like this:

from dagster import ConfigurableResource


import ftplib
from dagster import resource

class SppFTPConnection(ConfigurableResource):
    ftp_host: str

Running dagster dev I get the following error:
AttributeError: 'SppFTPConnection' object has no attribute '_state__internal__'
Am I missing something?