Google Api Search Result is not working - php

Question

To get the search result from google, I used those code. Sometimes it work perfectly but sometimes it don't give any answer. Now don't know what is the problem. I need those result for research purpose so I had to browse for different query
if (isset($_GET['content'])) {
// echo $_GET['content'];
$url_all=NULL;
$visibleurl=NULL;
$title_all=NULL;
$content_all=NULL;
$mainstring=NULL;
$searchTerm=$_GET['content'];
$endpoint = 'web';
$key= 'angelic-bazaar-111103';
$url = "http://ajax.googleapis.com/ajax/services/search/".$endpoint;
$args['q'] = $searchTerm;
$args['v'] = '1.0';
$url .= '?'.http_build_query($args, '', '&');
$url .="&rsz=". 8;
$ch = curl_init()or die("Cannot init");
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$body = curl_exec($ch)or die("cannot execute");
curl_close($ch);
$json = json_decode($body);
for($x=0;$x<count($json->responseData->results);$x++){
$url_all .="#$*##" . $json->responseData->results[$x]->url;
$visibleurl .="#$*##" . $json->responseData->results[$x]->visibleUrl;
$title_all .="#$*##" . $json->responseData->results[$x]->title;
$content_all .="#$*##" . $json->responseData->results[$x]->content;
}
**EDIT
This Code works well sometimes, other times it doesn't, Is it a problem of google or something else. I get this error
$json->responseData->results for this showing "Trying to get property of non-object in"