Problem with `unsupported_slash_commands`

[ellisonbg]

Description

When using the Jupyter AI 3.0.0a0 pre-release, I see the following exception in the terminal where I started JupyterLab

Context

I am using the following conda env:

name: jupyter-ai-testing
dependencies:
  - python
  - pip:
    - jupyterlab==4.2.5
    - jupyter-ai==3.0.0a0
    - langchain-aws

[dlqqq]

I've also encountered this issue when testing the pre-release. It seems to happen when a chat model isn't selected in the Jupyter AI settings.