自定义菜单没有返回正确json 对错码的数据包？

自定义菜单，数据正确，没有返回{"errcode":0,"errmsg":"ok"} 这个代码。返回的是NULL？怎么回事的？

最后代码：echo $postJson = urldecode(json_encode($postArr));
                 $res=$this->http_curl($url,'post','json',$postJson);
                  var_dump($res);

结果：{"button":[{"name":"菜单一","type":"click","key":"item1"},{"name":"菜单二","sub_button":[{"name":"歌曲","type":"click","key":"songs"},{"name":"电影","type":"view","url":"http:\/\/www.baidu.com"}]},{"name":"菜单三","type":"view","url":"http:\/\/www.qq.com"}]}NULL