Doesn't work with jupyter_collaboration

[keeganmccallum]

Hi there, when I try to use the extension with jupyter_collaboration enabled I get the folloing error:

[E 2023-08-11 10:52:15.662 YDocExtension] Error watching file: Untitled.ipynb
    TypeError("'<' not supported between instances of 'NoneType' and 'datetime.datetime'")
    Traceback (most recent call last):
      File "/home/anon/Downloads/invokeAI/installer_files/env/envs/py310/lib/python3.10/site-packages/jupyter_collaboration/loaders.py", line 170, in _watch_file
        await self.notify()
      File "/home/anon/Downloads/invokeAI/installer_files/env/envs/py310/lib/python3.10/site-packages/jupyter_collaboration/loaders.py", line 187, in notify
        await callback("metadata", model)
      File "/home/anon/Downloads/invokeAI/installer_files/env/envs/py310/lib/python3.10/site-packages/jupyter_collaboration/rooms.py", line 190, in _on_content_change
        if event == "metadata" and self._last_modified < args["last_modified"]:
    TypeError: '<' not supported between instances of 'NoneType' and 'datetime.datetime'