Unsupported operand type when destroying VM

[mainrs]

$ nixops destroy -d test
server> destroying VirtualBox VM...
Traceback (most recent call last):
  File "/nix/store/5glgnmqggmryrwzpi2vn1y0iiby8xg82-python3.8-nixops-2.0.0/bin/.nixops-wrapped", line 9, in <module>
    sys.exit(main())
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/__main__.py", line 710, in main
    args.op(args)
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/script_defs.py", line 661, in op_destroy
    depl.destroy_resources(
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/deployment.py", line 1610, in destroy_resources
    self.run_with_notify(
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/deployment.py", line 1468, in run_with_notify
    f()
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/deployment.py", line 1611, in <lambda>
    "destroy", lambda: self._destroy_resources(include, exclude, wipe)
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/deployment.py", line 1600, in _destroy_resources
    nixops.parallel.run_tasks(
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/parallel.py", line 106, in run_tasks
    raise list(exceptions.values())[0]
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/parallel.py", line 70, in thread_fun
    work_result = (worker_fun(t), None, t.name)
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/deployment.py", line 1591, in worker
    if m.destroy(wipe=wipe):
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixopsvbox/backends/virtualbox.py", line 621, in destroy
    nixops.known_hosts.update(self.private_ipv4, None, self.public_host_key)
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/known_hosts.py", line 71, in update
    add(new_address, public_host_key)
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/known_hosts.py", line 64, in add
    _rewrite(ip_address, True, public_host_key)
  File "/nix/store/ijv5jg62i5sbfs6p5amsk73a1g0ab435-python3-3.8.9-env/lib/python3.8/site-packages/nixops/known_hosts.py", line 48, in _rewrite
    new.append(ip_address + " " + public_host_key)
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

Not really sure what to add here... If you need anything, let me know!