Seems to fix to the hide non-existing issue

[clement-moulin-frier]

Description

@corentinlger This PR seems to fix to the hide non-existing issue #120 . In case you have time to have a quick look at it, can you tell me if you think it makes sense? (or more importantly, if you think it won't break anything else). Thanks :)
See "How to test" below.

Related Issue (if applicable)

#120

How to Test

• Start practical session 4
• Execute cells up to controller.run()
• Open the web interface
• Close the notebook session by executing the last cell of the session, but do not close the interface windows
• Restart the jupyter kernel and restart the session
• Execute cells up to controller.run()
• Refresh the interface windows.

Before this fix, we were having a RuntimeError: _pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes' in the last executed notebook cell. It shouldn't be the case now.

Also check that we don't see hidden entities in the interface (if it works, you should see 7 resources).

[corentinlger]

This seems to be a lot cleaner and works well on my WSL machine.

[corentinlger]

@clement-moulin-frier I couldn't reproduce the error with _pending_writes in the main branch on my WSL machine.

I think this new solution works, but the hide non existing was already working most of the time before I did the ugly fix with trigger_hide_non_existing. Unfortunately I didn't find any way of reproducing it consistently, so it's hard to tell if the problem is really fixed now.

It think should be safe to merge and if students still have problems, they can always untick / tick again the hide non existing button from the interface manually.

I hope this helps !

[clement-moulin-frier]

Thank you for having taken the time to have a look @corentinlger ! I'm merging it, worst case it will have no effect ;)