nil inside configureDefaultState method

[yurevich1]

To prevent 'fatalError' , add self.foregroundViewTop = top after

// add identifier
        let top = (foregroundView <- [Top(8)]).first
        top?.identifier = "ForegroundViewTop"

and self.containerViewTop = top after

// add identifier
        let top = (containerView <- [Top(8)]).first
        top?.identifier = "ContainerViewTop"

[xyfqldy]

Yes ,I met the same question