Jupyterhub running on docker + docker spawner - how to add volume

Question

I have a problem that I struggle with for a while and I hope somebody could give me a hand.

I'm using this simple configuration with one, small difference - here is my jupyterhub_config.py:

import os

# dummy for testing. Don't use this in production!
c.JupyterHub.authenticator_class = "tmpauthenticator.TmpAuthenticator"

# launch with docker
c.JupyterHub.spawner_class = 'dockerspawner.DockerSpawner'

# we need the hub to listen on all ips when it is in a container
c.JupyterHub.hub_ip = '0.0.0.0'
# the hostname/ip that should be used to connect to the hub
# this is usually the hub container's name
c.JupyterHub.hub_connect_ip = 'jupyterhub'

# pick a docker image. This should have the same version of jupyterhub
# in it as our Hub.
c.DockerSpawner.image = 'jupyter/scipy-notebook'

# tell the user containers to connect to our docker network
c.DockerSpawner.network_name = 'jupyterhub'

# delete containers when the stop
c.DockerSpawner.remove = True

And it works. Now I'd like to add some user volumes, by adding at the end of above config this:

c.DockerSpawner.volumes = {'/srv/jupyterhub/': '/home/jovyan/work'}


def create_dir_hook(spawner):
    """ Create directory """
    username = spawner.user.name  # get the username
    volume_path = os.path.join('/srv/jupyterhub', username)
    if not os.path.exists(volume_path):
        os.makedirs(volume_path, mode=0o755, exist_ok = True)

c.Spawner.pre_spawn_hook = create_dir_hook

But then I got this error:

Unhandled error starting d746c770-7eee-40fa-b073-97fe3a578569’s server: The ‘ip’ trait of a Server instance must be a unicode string, but a value of None <class ‘NoneType’> was specified.

Could someone help me and tell how to run this with user's volumes?