Using previous_post_link and next_post_link to wrap around post sequence

For a single custom post type, I’m using previous_post_link and next_post_link with simple arrows. (Although text arrows are shown here, in the actual I’m using graphics with the text hidden via CSS.) Code:

<nav class="arrowNav">
    <div class="nav-previous">
       <?php previous_post_link('%link', '«'); ?>
    </div>

    <div class="nav-next">
       <?php next_post_link('%link', '»'); ?>
    </div>
</nav>

This works fine except for the edge cases. I’d like the posts to wrap around: that is, for the first post, I’d like previous_post_link to link to the last post, and for the last post next_post_link would link to the first post. It appears the default for both those cases is null. How do I test for first and last post status and produce links for each?