Unexpectedly found nil while unwrapping an Optional value on `dismissCoordinator`

[YuantongL]

Found this in version 2.0 To replicate:

• Launch Stinsen example app
• Switch to TestBed tab
• Tap on "Modal Screen"
• Tap on "Dismiss me!"
• Observe Unexpectedly found nil while unwrapping an Optional value

[YuantongL]

Ah... use modal coordinator does not cause the error, I guess that was there for an bad example. My bad...