import java.util.List; import java.util.Optional; import java.util.function.Function; class Main { { List<Optional<Function<String, String>>> list = asList(of(Main::identity)); } static <T> List<T> asList(T... a) { return null;} static <T> Optional<T> of(T value) { return null;} public static String identity(final String s) { return s; } }