我没办法get_terms() 返回空条件，我已经尝试了很多方法。

代码如下：

$terms = get_terms(\'device\',array(\'hide_empty\' => 0));
foreach($terms as $term) {
        if($term->parent == 0) {
            if($i++ != 0) echo \'</optgroup>\'; echo \'<optgroup label="\'.$term->name.\'">\';
            $id = $term->term_id;
            $args = array("child_of"=>$id);
            $this_term = get_terms(\'device\',$args);
            foreach($this_term as $the_term) { 
                $term_name = str_replace($term->name,\'\',$the_term->name);
                echo \'<option value="\'.$the_term->term_id.\'">\'.$the_term->name.\'</option>\';
            }
        }
    }

我已经尝试了所有可能的方法：

$terms = get_terms(\'device\',array(\'hide_empty\' => false))
$terms = get_terms(\'device\',array(\'hide_empty\' => 0))
$terms = get_terms(\'device\',array(\'hide_empty=false\'))
$terms = get_terms(\'device\',array(\'hide_empty=0\'))

也尝试了最后两种方法array. 似乎什么都没用。它返回所有有帖子的术语，但没有空的。

$terms = get_terms( \'device\', array( \'hide_empty\' => false, \'parent\' => 0 ) );