How-to display author bio if it exists

In my single.php, I have a snippet that says if the post is in a particular category, then display the author’s bio. I’d like to place another IF statement to surround it so that if the author bio doesn’t exist then skip the whole thing. This is what I have

<?php
if (in_category(8)|in_category(9)|in_category(10)|in_category(11)|in_category(12)|in_category(14)|in_category(18))
{
echo ‘<h6>About the author</h6>’;
echo ‘<em style=”font-size:85%;”>’;
echo the_author_description();
echo ”;
}
?>

So I want to place an IF so that this will only execite if the author bio doesn’t equal null.

Thanks,
Carlos