Can't delete fieldset attached to deleted model

[thekanbo]

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What is the issue?

If a collection/matrix/taxonomy is deleted, but has a fieldset attached to it, the fieldset will then be unable to be deleted.

What are the steps to reproduce this issue?

1. Attach an existing fieldset to an existing matrix collection
2. Delete the matrix collection
3. Try and delete the fieldset

What were you expecting to happen?

The fieldset should successfully delete

Any logs, error output, etc?

Call to a member function detachFieldset() on null

/app/Observers/FieldsetObserver.php line 29

$model->detachFieldset();