Attribute 'title' has not default value if term description is left empty

This is against good SEO practice to leave empty the title attribute in a link. I suggest to put the term name instead if the description is not present:

function taxonomy_link($type, $node = NULL) { 
......
attributes' => array('rel' => 'tag', 'title' => ($term->description ? strip_tags($term->description) : $term->name))
......
}