There is no nil! However, "fatal error: unexpectedly found nil while unwrapping an Optional value"
I don't know why it's an error. without nil
There is no nil in the situation where you have to develop explosive speed in the limited time of the laboratory
The content of the error is
fatal error: unexpectedly found nil while unwrapping an Optional value.
I wonder why I didn't use ??? nil and I didn't force unwrap it. I missed such a place (； ∀ ；)
Solution
The quickest way is to re-link the outlets again.
How to check the association
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It's like an error that happens when the Outlet doesn't connect properly for some reason.
As a result, it is treated as if there is no UI such as Label/Button/TextField of UIKit. You will get an error warning with nil!
If you do it normally when linking UI with Outlet, it will never be nil.
In my case this was the solution! I hope it helps someone.