$questions may be 0 (Zero).
public function nav_link($navlink, $class) {
qa_html_theme_base::nav_link($navlink, $class);
if($class == 'browse-cat') {
echo 'label = '.$navlink['label']."<br/>"; // Category name
$questions = qa_db_single_select(qa_db_qs_selectspec(qa_get_logged_in_userid(), 'created', 0, $navlink['label'], null, false, false, 3));
echo 'questions = '.count($questions); // Result set
...
}