swift3 - iOS 10 请求授权

Question

我不知道这段代码有什么问题，它总是向我显示这个东西：fatal error: unexpectedly found nil while unwrapping an Optional value 当我尝试访问时，我得到了那个东西MPMediaLibrary，代码是这样的：

if (MPMediaLibrary.authorizationStatus() == MPMediaLibraryAuthorizationStatus.notDetermined) {

            // Access has not been determined.
            MPMediaLibrary.requestAuthorization({ (status: MPMediaLibraryAuthorizationStatus) in

                if (status == MPMediaLibraryAuthorizationStatus.authorized) {
                    let albumsQuery: MPMediaQuery = MPMediaQuery.albums()
                    let albumItems: [MPMediaItemCollection] = self.albumsQuery.collections! as [MPMediaItemCollection]
                }
            })
        }