.then closures not called

[olSolo]

Example:

MyModuleInput

protocol MyModuleInput: class {
    func configureModule(item: ARItemInfo)
}

Presetning module router:

            try self.transitionHandler!.forSegue(identifier: segueIdentifier, to: MyModuleInput.self).then({ (moduleInput) in
                moduleInput.configureModule(item: item)
            })

If MyModuleInput protocol is NOT defined as class, the .then block will not be invoked.
I think there must be some kind of warning or a check for this case