Where are you executing that code?
rows cant be nil so the screenletview is the nil here, maybe its not yet initialized

 // On List item selection
    func screenlet(screenlet: NewsListScreenlet,
        onNewsSelectedEntry entry: NewsListScreenletEntry) {
       
        // open page view controller
        let mainStoryBoard : UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
        let viewController : PageViewController = mainStoryBoard.instantiateViewControllerWithIdentifier("PageViewController") as! PageViewController
        let rows = (screenlet.screenletView as? BaseListView)?.rows
        print("selectedrows" , rows)
        // viewController.rows = rows
        if let rowCount = (screenlet.screenletView as? BaseListView)?.rowCount {
            viewController.rowCount = rowCount
        } else {
            viewController.rowCount = rows?.count ?? 0
        }
        
        viewController.selectedEntry = entry
        viewController.pageType = menuItem.pageType
        viewController.contentType = menuItem.friendlyURL
}
    }