PHP表单select中有0选项的处理

<div class="layui-inline">
    <label class="layui-form-label">是否锁定</label>
    <select class="layui-select" name="is_lock" id="is_lock">
        <option value="">-请选择-</option>
        <volist name="lock_id_name" id="vo">
        <option value="{$vo.id}" <?php if($is_lock === $vo['id']){echo "selected";} ?>>{$vo.name}</option>
        </volist>
    </select>
</div>

if ($_GET['is_lock'] ||  $_GET['is_lock'] !== NULL) {
    $where['is_lock'] = $_GET['is_lock'];
    $this->assign('is_lock', (int)$_GET['is_lock']);
}

经过上面的恒等于处理！可以判断出0！
通过下面的不等于NULL，可以判断出空。