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