public class Bug<T> { 
    public T invoke(Object... args) { 
        return null; 
    } 
    public static <T extends String> void test() { // works with <T> alone. 
        Bug<T> bug = new Bug<>(); 
        java.util.function.Function<String, T> b = bug::invoke; // compile error, but works with (args) -> bug.invoke(args); 
    } 
}