php中json转数组失败，大佬们帮看下什么原因，蟹蟹

这是后台代码：

    $ls = $_GPC['goods'];
    $lss = '[
    {"count":1,"options":[],"hasoption":"0","goodsid":"159","name":"冰红茶","is_pbox":"0","pbox_price":0,"totalprice":"3.00","marketprice":"3.00"},
    {"count":1,"options":[],"hasoption":"0","goodsid":"160","name":"脉动","is_pbox":"0","pbox_price":0,"totalprice":"4.00","marketprice":"4.00"}
    ]';
    echo "<pre>";
    var_dump($ls);
    var_dump(json_decode($ls,true));
    var_dump(json_decode($lss,true));

$lss是一个合格的json，$ls是前台传过来的json；
下面是输出：

第一个打印值是前台传的json，这个json无法转数组，第二个红圈值空是前台json转数组，第三个是模拟json转数组，现在这个前台传的json为空的未发现原因！