why is a link not generated although there is the href?

This is my code, even if i used href with the tag in the list there isn't the link.

Html code:

<ul>

        <li th:each="author : ${authors}">
            <a th:href="@{ '/author' + '/' + ${author.id} }" 
                   th:text="${author.firstname} + ' ' + ${author.lastname}"></a>
        </ul>

My controller:

@RequestMapping(value="/author/{id}", method=RequestMethod.GET)
public ModelAndView getAuthor(@PathVariable("id") Long id) {
    ModelAndView m = new ModelAndView();
    if (id != null) {
        Author a = this.authorService.authorPerId(id);
        m.addObject("author", a);
    } else {
        m.addObject("author", new Author());
    }
    m.setViewName("author/get");
    return m;
}